Abstract The current method for monitoring cyclosporine measures predose concentrations (C 0). A better method has been developed, namely, measurement of the blood cyclosporine concentration at 2 hours postdose (C 2). The aim of this survey was to determine the variability of C 0 and C 2 concentrations among stable renal transplant patients. One hundred two stable renal transplant patients who were at least 6 months posttransplant were recruited from the renal transplant outpatient clinic. The cyclosporine dose was between 100 and 500 mg daily; all patients had been monitored using C 0 concentrations. Blood samples for cyclosporine concentration measurements were taken at both C 0 and C 2 at two consecutive clinic visits. The within- and between-patient variabilities were calculated using nested analysis of variance. The mean age was 50 years (21 to 81); the mean weight was 75 kg. The mean cyclosporine dose was 3.18 mg/kg/d (1.2 to 8.8). The average serum creatinine was 174 μmol/L (77 to 626) and the average cholesterol was 5 μmol/L (3 to 9). The mean (±SD) C 0 concentration was 150 (47.31) μg/L and C 2 = 895 (239) μg/L. The C 0 concentration varied over 16-fold between patients compared to a sevenfold variation in C 2. The between-subject coefficient of variation (CV) was 35% for C 0 and 30% for C 2 and the within subject CV was 23% for C 0 and 20% for C 2. The results suggest that cyclosporine concentrations at C 0 are slightly more variable than those at C 2. Whether this modest reduction in variability results in better patient outcomes is the subject of the next phase of this study.