This study examined perceptions of ideal and actual function in the “big brother” role amongst big brothers, single-parent mothers, social workers and a control group. In the ideal perspective, sinele-went mothers and social workers valued the family substitute aspect bf the big brother role as significantly more important than did bie brothers. Perceotions of actual function wihin JTOUDS showed that big brothers perceived themselves as doing less couseling activity and somewhat more family substitute activity than their professed role ideals. It was suggested that the single-parent mothers’ sigruficantly stronger role ideal for family substitute activity may be related to less counseling activity in big brothers. Implications of these findings for program effectiveness and future research are discussed.