In the presence of impaired renal function a number of pharmacologic agents require dose adjustments to avoid toxicity. Physician dose variations of a wide range of pharmaceuticals, 237 orders for 30 drugs for 107 patients, were compared to doses recommended by a computer program which considers renal function in calculating its dose. Disagreement in dose regimens was evaluated by comparison of physician-dose to computer-dose for three classes of drugs: wide range, narrow range, and 80% renally excreted. With true renal impairment (serum creatinine ≥1.2 mg/100 ml and creatinine clearance <80 ml/m) significant overdosing occurred for narrow range and 80% renally-excreted agents, 83 and 77% respectively. There is a great potential hazard observed to be avoided. It is recommended that dose adjustments for nephrotoxic or renally-exereted agents be implemented using creatinine clearance (estimated or measured) with, at the very least, manufacturer's recommendations.