As a result all new research at the center has been halted.

This week's death will be part of an investigation the U.S. Department of Agriculture had already undertaken to determine what, if any, penalties will be imposed on Harvard Medical School.

“Four deaths in the last 18 months or so, that's unacceptable. They know they need to do better,” USDA spokesman David Sacks said. (The USDA) “is looking at penalty actions as a result of this, but that investigation has not been completed yet. We will continue to closely monitor them and see that they right their ship ... and get back on proper footing of giving these animals humane care, which I know is what they intend to do.”

Dr. Jeffrey S. Flier, dean of the faculty of medicine at Harvard Medical School, in an email sent to the Telegram & Gazette yesterday, said new research has been stopped to allow time for personnel to create and implement a corrective action plan.

“I care deeply about this issue. The health and ethical treatment of the primates for which we are responsible are among my highest concerns. I want to assure you that the leadership of HMS will be unwavering in our commitment to providing for the welfare of these animals,” he said.

Mr. Sacks said Harvard, as with the other three deaths, self-reported the death that occurred Sunday to one of the USDA's inspectors. He said the federal Animal Welfare Act does not require research centers to report deaths partly because some animals die from natural causes and others die as a result of the research. The Animal Welfare Act, passed by Congress in 1966, requires research facilities to provide their animals with adequate care and treatment in the areas of housing, handling, sanitation, nutrition, water, veterinary care, and protection from extreme weather and temperatures.

Mr. Sacks said he is not sure of the circumstances surrounding the latest death. The Boston Globe, however, reported that a Harvard Medical School official said the elderly cotton top tamarin monkey likely died from a lack of water because it did not have a water bottle in its cage. Mr. Sacks said a USDA inspector will go to the center within the next several days.

The previous deaths occurred in June 2010, and October and December 2011. In the first incident, a monkey was found dead at the bottom of a cage washer after having gone through the washer. In October, a monkey escaped while being taken to a research procedure. It was caught, taken to the procedure and later found dead after being returned to its cage. On Dec. 26, a monkey died of dehydration after a water dispenser was not properly activated. That death was cited in a Jan. 31 USDA inspection report that also said a second monkey was dehydrated but survived. Two other non-compliances involved a monkey suffering a broken leg when the leg was caught under the drop door as it closed; and another injured its foot after it and several other monkeys were able to open the cage that was not properly secured and get outside.

Harvard Medical School said several aggressive steps and corrective measures have been put in place since last summer, including the creation of a quality control unit as a safety net, increased oversight at all levels, staff retraining, implementation of new systems and system redundancies, and MRI testing to improve monitoring and reporting. In September, a new director, interim associate director for administration and veterinary leadership were also brought on board at the research center.

Dr. Flier said the school will build upon those measures.

“I am personally marshaling all necessary resources to confront and resolve the systems, processes and human errors that appear to underlie the recent problems,” he said.

The additional corrective measures include the establishment of another oversight team of veterinary staff and supervisors who will perform additional daily rounds to verify the health and wellness of every animal at the center. The school is also assembling an independent review committee of external prominent experts to assess the primate's center's operations and to help develop a strategy to ensure similar problems don't occur. Co-reporting lines have also been established. The center's director and associate director are now required to report to senior leadership at the medical school, Dr. Flier noted.

Michael Budkie, spokesman for the Ohio-based watchdog group Stop Animal Exploitation Now, said he thinks even more needs to be done. He said the USDA should impose a fine on Harvard Medical School. He said that since 1986 when he started as an animal rights activist, he has never seen a research facility that has had as many negligent deaths of animals in such a short period of time. Harvard has received official warnings in the past, but to his knowledge, never a fine. He said that the National Institutes of Health, which provides the center with research grants, should also be involved in the investigation.

The New England Primate Research Center was established by Congress in 1962 and is one of eight regional primate centers in the country. The sprawling campus, tucked away in the woods from view of passers-by, is on 89 acres in Southboro and 42 acres in neighboring Marlboro, off Parmenter Road near Callahan State Park. According to its website, the center is a leader in primate biomedical research and has provided scientific resources and services to investigators throughout the world.

Dr. Flier said the center's mission is to eradicate disease. Key discoveries enabled by the center have contributed to the understanding of HIV/AIDS, colon cancer, sickle cell anemia, herpes virus, inflammatory bowel disease and Parkinson's disease among other disorders, he said.