This study examined the dose-effect relationship between the number of sessions and therapeutic outcome in a large, nationwide counseling center research consortium. A positive relationship was found between the outcome of counseling and the number of sessions attended. The results of this study support the effectiveness of brief psychotherapy. In recent years, the dose-response metaphor borrowed from pharmacology research has gained prominence in psychotherapy outcome research, as well (see Jones, Bigelow, & Preston, 1999, for example). One of the major contributions to this type of research is the influential meta-analysis performed by Howard, Kopta, Krause, and Orlinsky (1986), who proposed a doseeffect model linking the dosage of therapy sessions attended to the improvement clients experienced by attending each session. The log of the number of sessions became the dose, and the normalized probability of improvement was defined as the effect, using probits as the unit of analysis. The researchers constructed their dosage model by probit analysis of 15 previous outcome studies, some dating as far back as 1950, and computed the predicted improvement session by session. The results verified that the longer patients remained in therapy, the greater the gain. Results also revealed that 15% of patients improve between intake and the first session (presumably due to spontaneous remission and the ameliorative effects of having sought treatment), 50% improve after 8 sessions, and 75% improve after 26 sessions. Inspired by these results, other researchers began to analyze the dose effect for