Although the majority of prevention efforts have focused on women, reduction of heterosexual transmission of STDs also requires interventions for men, necessitating understanding of men's safer sex decision making. In a random sample of 486 heterosexually active men, the theory of reasoned action (TRA) was used to predict intentions to use condoms with casual partners, as well as 2 steady-partner safer sex behaviors: mutual monogamy and condom use. The basic TRA model fit the data well. Expanded models identified the mediated (via attitudes, social norms, and self-efficacy) and, for some, direct effects on intentions and behavior of selected intrapersonal, interpersonal, and sociocultural variables. Results suggest that the role of external variables might vary depending on the behaviors in question.