The aim of this study was to develop and test a descriptive, intensive drug surveillance methodology in order to examine the effectiveness and safety of new drugs in the immediate postmarketing period. The HMG-CoA reductase inhibitor, simvastatin (Zocor), was chosen as the test drug. Data were collected from 100 randomly chosen cardiologists, specialist physicians and general practitioners practising in the six main centres of South Africa. A 66% doctor response rate was achieved and 438 patients were enrolled in the study. The overall effectiveness expressed as a percentage decrease (from baseline) in total cholesterol levels was 20.5% for the 251 patients who started on a 10 mg daily dose of the drug and 27.6% for the 42 patients who started on 10 mg but changed to 20 mg/d. The safety profile of simvastatin was comparable with the premarketing clinical trial data, and patient non-compliance appeared to be dose-related. The methodology employed was found to be suitable for the collection of safety and effectiveness data in the postmarketing period and simvastatin was shown to be effective with few adverse events reported.