During treatment, the therapeutic alliance is characterized by rupture and repair episodes, which in turn are associated with psychotherapy outcome. It would be important to have a parsimonious tool to identify ruptures in psychotherapy sessions to provide therapists with meaningful feedback about when they occur. The present study thus aims to establish whether measuring self-reported alliance dynamics can function as a measure of alliance ruptures. The sample consisted of 58 depressed patients, who received 22 sessions of cognitive therapy for depression in an outpatient setting. The observer-rated Rupture Resolution Rating System (3RS) was applied to 58 sessions where the self-reported Working Alliance Inventory (WAI) completed by patients after each therapy session indicated that alliance ratings declined more than 2 SDs from that patient's individual mean. For comparison purposes, the 3RS was also applied to 58 randomly chosen sessions from the same treatment phase (early, middle, late). Results showed significant differences between sessions where the WAI indicated a drop in the alliance and randomly chosen sessions of the same treatment phase with regard to the frequency and impact of ruptures. This speaks for the construct validity of the 3RS. Session-by-session alliance ruptures may reliably be measured using a case-sensitive approach to identify meaningful drops in alliance self-report (WAI). (PsycInfo Database Record (c) 2024 APA, all rights reserved).