The purpose of the present study was to determine whether the availability of results from a high-sensitivity, rapid test for group A streptococci (Strep A OIA; BioStar, Inc., Boulder, Colo.) improves physician outcome. The study population included 465 consecutive patients with symptoms of acute pharyngitis seen in two outpatient clinics in a large suburban medical center; one clinic, a walk-in clinic (WIC), primarily saw adult patients, and one clinic, a pediatric and adolescent medicine clinic (PED), primarily saw pediatric patients. We measured improvement in physician outcome by comparing physician intent for prescribing an antibiotic based on clinical impression with physician practice once the results of the Strep A OIA were known. Based upon intent, the physicians seeing WIC patients (WIC physicians) would have prescribed an appropriate antibiotic course for 42% of patients with cultures positive for group A beta-hemolytic streptococci (GABHS) and 61% of patients with cultures negative for GABHS. After receiving the results of the Strep A OIA, WIC physicians prescribed an appropriate antibiotic course for 81% of patients with positive cultures and 72% of patients with negative cultures. Based upon intent, the physicians seeing PED patients (PED physicians) would have prescribed an appropriate antibiotic course for 35% of patients with positive cultures and 77% of patients with negative cultures. After receiving the results of the Strep A OIA, PED physicians prescribed an appropriate antibiotic course for 90% of patients with positive cultures and 81% of patients with negative cultures. Based on a 14.5% prevalence of GABHS among WIC patients, Strep A OIA improved the overall WIC physician outcome from 58 to 74%. Based on a 31.5% prevalence of GABHS among PED patients, Strep A OIA improved the PED physician outcome from 64 to 84%. Had Strep A OIA alone guided therapeutic choice, physicians would have prescribed an appropriate antibiotic course for 95% of the patients at the time of the initial encounter. We conclude that the use of Strep A OIA improves physician outcome.