The social learning approach to marital and family therapy is a didactic approach calling for an active and directive therapist and a collaborative client. To examine the variability of therapist and client behaviors within sessions and across the course of treatment, 24 families, in marital and family therapy, participated in the study. Families were randomly assigned to either a marital-then-family therapy sequence or a family-then-marital therapy sequence. Ten therapy sessions were audiotaped and coded for seven therapist and seven client behaviors across three phases of treatment: beginning, sessions 1-3; middle, sessions 4-7; end, sessions 8-10. An analysis of the results showed that encouragement of affective expression was the only therapist behavior that changed across time, starting with low frequency, increasing in the second phase, and decreasing in the third phase. Client measures which changed across time included blame, task orientation, mutuality, and tone. One of the therapist behaviors, encouragement of specificity and clarity, and three of the client behaviors, emergency emotions, welfare emotions, and tone, varied significantly within the treatment sessions. Detailed correlational analyses provided a description of the relationship between therapists' and clients' session behaviors. These findings support a social learning approach to marital and family therapy. (BL)