A systematic study of judgements of social interactions along a friendly-unfriendly dimension revealed marked cross-sex differences. With same-sex judgements, males judging male interactions and females judging females, no difference was found. In their judgements of female interactions, however, male judgements were linearly related to female judgements, but the latter scale had a far wider range. In their judgement of male interactions, females had a comparatively restricted range for friendly interactions, but differentiated as well as males in the very unfriendly range. Implications of these findings for systematic observation techniques are outlined and some implications of sex differences in social perception discussed.