An innovative psychotherapy process research methodology that combines Interpersonal Process Recall with Repertory Grid analysis is introduced. This methodology was employed to examine the construct systems used by a therapist to make client behaviors meaningful. The therapist's construct systems varied across the three interviews studied. In the interview during which the therapist was judged to be most effective, the construct system used evidenced a higher level of cognitive complexity than the construct systems used in the other two interviews. Research applications of the methodology are discussed.