An Institute of Medicine (IOM) committee that is studying whether the United States should continue to fund chimpanzee research last month saw two of its provisional members withdraw, after animal welfare activists raised questions about their ability to be objective.

Now, the committee’s chair, John Stobo, the senior vice president for health sciences and services at the University of California, has also withdrawn from the committee. This listing of current committee members notes that he withdrew on June 8.

Stobo, who ran the committee’s first meeting late last month, referred questions about his departure to the IOM, where spokeswoman Christine Stencel said by e-mail: “The review process is confidential. We appreciate Dr. Stobo’s willingness to share his time and expertise.”

She added: “The committee appointment process is a dynamic process that involves public feedback to a list of provisional committee members as well as internal review of their expertise, interest in serving, and any possible conflict of interest, whether perceived or actual. As a result of this multifaceted process, it was mutually determined that Dr. Stobo would not serve on the committee after all.”

Stencel said that the IOM expects to name a new chair in the next few days.

Animal rights activists, who have filed complaints about several committee members, but not Stobo, were bemused.

“We unfortunately do not have any sense of why he is no longer on the committee,” said Jeanne Stuart McVey, a spokeswoman for the Physicians Committee for Responsible Medicine.

Added Andrew Rowan, the chief scientific officer at the Humane Society of the United States: “It may simply be that he decided to withdraw. An [IOM] committee chair has a fairly onerous job, especially when the topic is controversial in the way this one is.”

Public comments on the remaining 12 committee members continue to be accepted; hit the “feedback” button at the bottom of this link.