The study tested the Andersen-Newman causal model of social service use as a means of determining patterns for social service use by Mexican American elderly. The model was shown to have applicability for identifying common and unique determinants of service use. Thirty-seven variables and data from a 1979-80 15-state survey were selected to form a subset of responses from 1,164 noninstitutionalized Mexican or Mexican American individuals aged 55 and over. Four variables were found to directly affect use of social services: knowledge of social services, need, health status, and income. The primary role of knowledge of services which emerged from the study was shown to have policy and administrative implications and it was suggested that more attention be focused on information processing activities and referral techniques. Tables of variables, relationships, systems utilization models, and individual determinants, and a 42-item bibliography are appended. (LFL)