The study was conducted in 43 library work groups. Supervisory role performances were measured by averaging questionnaire responses gathered from each group's members. Group performance was measured by questionnaire responses gathered from the supervisors of the groups. (The supervisors'performance assessments were tested against the members'perceptions, absence rates, and group ratings provided by the top executive staff of the library system). The study identified eight leadership functions which are performed differentially by the supervisors of the groups. Four of these role performances are related to the index of group performance. Two of the supervisors’activities, staffing and training, control major portions of the variance in group performanc