OBJECTIVES: The aims of this study were to document the number of clinical interventions conducted by pharmacists in an ambulatory setting and determine their effectiveness. METHODS: A pharmacy documentation form was developed and distributed to all Kelsey Seybold pharmacies in the Houston area. Kelsey Seybold Clinics is one of the largest IPA in the region. Pharmacists completed this form whenever they performed an activity outside the normal procedures required to fill a prescription. The form was designed to record five main activities categorized as: interventions, therapeutic interchanges, medication errors, adverse drug reactions and drug information questions. The pharmacists also recorded actions they took, recommendations made, and the results of the intervention. The time taken by the pharmacist to perform these interventions was also recorded along with demographic information of the patients. Data were coded and analyzed using SAS statistical package at a set priori significance level of 0.05. Descriptive and correlation analysis were carried out on the data collected. RESULTS: A total of 982 completed forms were obtained for a period of 6 months (May-October 2002). Most interventions (38.9%) were completed within 5 minutes and 30% were completed between 5 to 10 minutes. Pharmacists spent majority of their time on intervention activities (76.27%). Of the 749 interventions classified, they were categorized as therapeutic (14.98%), prescriptions (41.21%), insurance (40.07%), and compliance types (3.75%). Out of the 206 recommendations made by the pharmacists, 96% were accepted by the physicians. Interventions resulted in 30% of the drugs being clarified before being dispensed, while an additional 47% were changed before being dispensed. A negative correlation was seen between prescription volume and interventions. CONCLUSIONS: Pharmacists performed numerous interventions to maximize drug therapy outcomes. Intervention by pharmacists resulted in enhancing appropriate drug use thus reducing cost.