The veteran actor, a longtime animal rights campaigner, will head to Capitol Hill to moderate a congressional briefing on the National Institutes of Health's (Nih) maternal-deprivation research on baby monkeys.
He will join a panel of experts to argue that the experiments are cruel and unnecessary as the impact of mental illness on monkeys is not applicable to human health.
They will also outline other non-animal research methods scientists can use in place of animal testing.
A statement issued by Cromwell via People for the Ethical Treatment of Animals (Peta) reads: "By the time you get to be my age, you start to think that maybe you've seen it all - and then you realise that you haven't. When I first heard that Peta had released videos of maternal deprivation experiments on baby monkeys, I guessed it was some kind of retrospective.
"These barbaric experiments weren't justifiable 60 years ago. They certainly aren't justified in the 21st century, and they do not deserve the support of Congress and taxpayers."