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 sigruf~cantly more import& than did bie brothers. Perceotions of actual function wihin JTOUDS showed that big brothers perc&ved themselves as doing less cou&eling 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. [Arricle copies available from The Haworth Document Delivery Service: 1-800-342-%78.]