PETA Director of Laboratory Investigations Kathy Guillermo is responsible for uncovering abuses in laboratories, working with whistleblowers to expose violations of animal protection laws, seeking prosecution of abusers by federal and state agencies, and replacing animals in laboratories with modern, non-animal methods of experimentation.

A 19-year veteran of PETA, Guillermo was originally hired to head PETA's cosmetics-testing campaign in 1989. She spearheaded efforts to persuade major corporations— including Estée Lauder and Gillette—to declare permanent bans on all animal tests. In the first three years of the campaign, PETA's list of cruelty-free companies grew from 50 companies to more than 300. Under Guillermo's direction, the campaign drew headlines for staging colorful events, such as hanging banners from the Eiffel Tower and the Brooklyn Bridge and enlisting the aid of celebrities including Sir Paul McCartney, Linda McCartney, Kevin Nealon, and Kim Basinger.

Guillermo's 1993 book, Monkey Business: The Disturbing Case That Launched the Animal Rights Movement (National Press Books, foreword by Oliver Stone), details the cruelty case that first brought then-fledgling PETA into national prominence. The landmark Silver Spring monkeys case also led to the first-ever conviction of an animal experimenter on cruelty-to-animals charges.

Guillermo graduated with highest honors from the University of California at Berkeley in 1981. For several years before joining PETA, she worked as a spokesperson for one of the country's largest animal shelters. She is married to award-winning journalist Emil Guillermo and has three children and five rescued dogs.