Between April 1991 and February 1992 we obtained 87 percutaneous core needle biopsy specimens from 60 patients with the automatic biopsy gun. In 78 cases (89.7%) enough renal tissue was obtained for histological analysis. Acute rejection was present on 35 biopsies (40.3%) indicating antirejection therapy. No pathological signs of rejection were detected on 43 biopsies (49.4%). In 38 instances (43.7%) biopsy diagnosis differed from clinical presumptive diagnosis, affecting patient management, while in the remainder it was helpful to confirm clinical impressions. The only complication of the procedure was gross hematuria (requiring vesical irrigation in 1 patient). Due to its simplicity and low morbidity rate, renal biopsy with the automated needle system is the procedure of choice for evaluation and management of renal allograft dysfunction.