Hillier began teaching at the University of Washington as a research associate professor of obstetrics, gynecology and microbiology, before joining the faculty at the University of Pittsburgh (Pitt) in 1995.[4] While at Pitt, Hillier continued her study into HIV and Aids and founded the Microbiocide Trials Network (MTN), an international research program which studies ways to stop transmission of sexually transmitted diseases.[5] After a failed study conducted in 2001 showed nonoxynol did not prevent HIV infections, her project tried studies on spermicides and substances designed to block the entry of viruses into cells, both of which failed.[3] During this time, she was appointed president of the Infectious Diseases Society for Obstetrics and Gynecology and sat on the board of the International Society for Sexually Transmitted Disease Research.[6]