Comparatively little is known about how U.S. adult men's attitudes and characteristics influence their decision to use contraceptives to prevent pregnancy and to take actions to protect themselves from infection with sexually transmitted diseases (STDs). Attitudinal and background data on 1,595 men from the 1991 and 1993 waves of the National Survey of Men (NSM) were used, through logistic regression techniques, to predict the likelihood of current contraceptive use to prevent pregnancy and recent efforts to avoid STD infection among men in three types of sexual relationship--marriage, cohabitation and dating. At the 1993 interview, 58% of men were using contraceptives to prevent pregnancy and 22% had recently taken actions to protect themselves from STDs. Men's concern about how easy a method was to use reduced the likelihood of STD protection, but had no influence on contraceptive use to prevent pregnancy; however, concerns about a method's risks to the female partner increased the likelihood of both outcomes. Couples in which the man expected his partner to take primary responsibility for contraception were 40% as likely to be protecting themselves against STDs as were couples in which the man believed he shared or had greater responsibility. Married men were the least likely to be protecting themselves against STDs, whereas men who were dating were the most likely to do so. Men's attitudes and characteristics were important predictors of contraceptive use to prevent pregnancy and of efforts to protect against STDs, even after controls for the female partner's characteristics were entered in the analysis. The findings emphasize the need to include men in interventions aimed at reducing unintended pregnancy and STD transmission.