Transplant patients receiving the immunosuppressive drug cyclosporin A require regular monitoring to maintain levels within a narrow therapeutic range. A stable, accurate and reproducible high-performance liquid chromatographic method for analysis of cyclosporin A in whole blood has been developed using the Varian Advanced Automated Sample Processor. Starting with 200 microliters of blood, absolute recovery of both cyclosporin A and the internal standard was 81% with a detection limit of 12.5 ng/ml. The assay is perfectly linear over the range 0-1000 ng/ml (r2 = 1.0). At a concentration of 250 ng/ml, the coefficient of variation, both between samples and between assays, is 1.87%. Chromatographic cycle time is 10.2 min per sample. Up to eighty samples can be processed by one person in a working day, with final results within 16 h.