Thirteen homosexual men, volunteers in a study of the natural history of HIV, who seroconverted to HIV after participating in an educational program on HIV prevention, were interviewed about the circumstances leading to their seroconversion. Six men had participated in unprotected anal intercourse with at least one partner whom they believed was HIV-negative. Four men attributed their conversion to mental health problems or to drug and alcohol use. Two men's seroconversions could not be ascertained and one man attributed seroconversion to a condom break. Most men who had learned how to avoid infection, and had successfully done so for a time, had knowingly engaged in unsafe behaviors because of strong emotional responses to certain partners or because of mental health or drug and alcohol-related problems. Skills training for dealing with partners who pressure men to behave unsafely is needed, as is mental health and drug and alcohol counseling for men at risk for HIV infection.