The safety and tolerability of transferring maintained renal transplant patients from Sandimmun to Neoral is being assessed in a multicentre, open-label, single-arm study. A total of 250 patients has been enrolled and results are available from 75 patients up to 12 months post-transfer. A slight trend to higher mean cyclosporin trough levels was seen in this cohort, but trough levels were unchanged in the sub-group receiving > or = 1 dose changes. The mean dose fell by 13%. Creatinine levels showed a slight overall upward trend. Blood pressure and uric acid were unchanged and adverse events were typical of those seen with Sandimmun. Neoral was well-tolerated. Data from the full cohort of 250 patients up to 3 months post-transfer support these findings. These results indicate that transfer from Sandimmun to Neoral is safe and well-tolerated and provides appropriate immunosuppression at a lower average dose than Sandimmun. The Neoral dose should be adjusted promptly, as required, to maintain the target trough level.