This multimethod study explored challenges faced by women in close heterosexual relationships who decided to test for HIV, and their experiences with instituting safer sexual practices and partner testing. Eighty-one women who sought HIV counseling and testing and had a regular male sexual partner were interviewed on five occasions, and 18 of these women and 15 men later took part in one of four focus groups (women only, men only, or couples). Findings identified difficulty understanding the unpredictability of HIV transmission, gender differences in how partners interpret their susceptibility to HIV, and male resistance to safer sex and testing. We also identified a pervasive phenomenon of "testing by proxy"--the belief that if one partner tests negative for HIV after having unprotected intercourse, the untested partner's serostatus is deemed to be negative. This dangerous practice must be addressed in public health prevention efforts. Programs aiming to reduce heterosexual HIV risk for women must include their male partners and incorporate effective interpersonal communication skills.