Eighty female Ss took part in a study of "impression formation", during which they evaluated a hypothetical stranger who was presented as either similar or dissimilar in opinions to themselves and as either having many socially desirable opinions or having many socially undesirable ones. Ss were then asked to rate on the Interpersonal Judgment Scale the stranger´s intelligence, knowledge of current events, morality, adjustment, attractiveness, and similarity in opinions to themselves, and to indicate their willingness to have the stranger as their intimate friend. It was found that both opinion similarity and opinion social desirability had a significant effect on interpersonal attraction. This finding seems to suggest that opinion similarity is a positively evaluated attribute or a reinforcing stimulus. It was also found that when the stranger was believed to have many socially desirable opinions, Ss tended to prefer the stranger similar in opinions to the one dissimilar in opinions as their intimate friend. On the other hand, when the stranger was perceived as having many socially undesirable opinions, Ss showed only a nonsignificant preference to have the stranger dissimilar in opinions as their intimate friend. The nonsignificant difference was attributed to Ss´ superficial involvement and the positively evaluated or the reinforcing nature of opinion similarity.