Programs which provide income maintenance to disabled persons of working age are experiencing rapidly growing enrollments and rising costs. Changes in the definition of disability are thought to be a contributing factor. A review of existing income programs for the work-disabled indicated that social and economic factors were used increasingly in disability determinations. In this study, five factors (functional limitation, age, occupation, sex, and education) were selected for study of their importance to lay persons in the definition of disability. College students (N=108) assigned levels of disability benefits appropriate for fictional applicants for public assistance disability benefits described in vignettes. Subjects used a scale ranging from not eligible to eligible for permanent lifetime benefits. The study used a factorial design to examine the relative importance of the five factors. Four of the five factors studied were found to exert important independent influences on the determination of disability. Functional limitation was of greatest importance, followed by age, occupation, and education. Sex had no significant impact. These results support the view that lay opinion sees disability as a condition defined by factors other than functional limitation. Further research might examine other factors which may also influence lay determinations of disability. (ABL)