The effects of short-term social support on cortisol levels and subjective responses to acute psychological stress were investigated in healthy adults (total N = 66). In anticipation of a public-speaking task in front of an audience, subjects received either no social support ("no support") or social support from an opposite-sex stranger ("stranger") or from their boyfriend or girlfriend ("partner"). Support providers were instructed to enact both instrumental and emotional support during the 10-minute anticipation period. The results obtained suggest sex-specific effects of social support. Although men in the partner support condition showed significant attenuation of cortisol responses compared with unsupported and stranger-supported men, women showed no response decrement under stranger support. In contrast to men, women showed a tendency toward increased cortisol responses when supported by their boyfriends. The endocrine response differences between male and female subjects were unrelated to questionnaire-derived psychological variables. No sex and group differences in perceived stress, mood changes, or social desirability were observed. Although the overall level of subjective well-being throughout the experiment was elevated in the partner support condition, no sex or group differences were observed in perceived stress, well-being changes, and social desirability. Opposite to their cortisol responses, women rated both stranger and partner support attempts more favorably than did men. No significant correlations were observed between the perceived stressfulness of the situation, mood changes, and cortisol responses. These results provide preliminary evidence for sex-specific patterns of social support efficacy to acute psychological stress with respect to adrenocortical responses.