This longitudinal study investigated physical therapists' perceptions of the roles of physical therapist assistants (PTAs). In 1986, a questionnaire describing 79 physical therapy activities was distributed to a random sample (n = 400) of physical therapists derived from the American Physical Therapy Association (APTA) membership. In 1992, a similar questionnaire was distributed to a representative sample (n = 400) of physical therapists derived from the APTA membership. Response rates were 53% and 55% in 1986 and 1992, respectively. Respondents indicated whether each activity was included in the documentation describing PTA roles. Results revealed considerable agreement between therapists' perceptions of PTA roles and those outlined by PTA practice guidelines, and these perceptions changed little over time. Discriminant analyses suggested that therapists' perceptions of PTA roles were, in general, not predicted by supervisory experience with PTAs, therapist experience, or content of entry-level professional education curricula. Generally, therapists' perceptions of PTA roles are consistent with published practice guidelines. Therapists' perceptions on selected activities, however, were incongruent with PTA practice guidelines, suggesting the potential for inefficient or inappropriate utilization of the PTA in the delivery of selected services.