The safety and tolerability of a microemulsion formulation of cyclosporin A (Sandimmun Neoral) in 20 post-renal transplant patients with stable allograft function was studied. The conventional formulation of cyclosporin A (Sandimmun) was converted to the microemulsion formulation using a ratio of 1:1. The patients were followed up for 12 weeks and their vital signs and safety parameters were monitored. After the conversion, there was no significant change in the mean cyclosporin dose given and mean cyclosporin levels (180 +/- 54 ng/mL at week 0 vs 172 +/- 42 ng/mL at week 12). Both serum creatinine and blood pressure remained stable (128 +/- 18 microgram/mL at week 0 vs 126 +/- 20 microgram/mL at week 12 and 99 +/- 10 mm Hg at week 0 vs 98 +/- 9 mm Hg at week 12). Only two adverse events were reported and no acute rejection episode was recorded. We believe that the conversion of the conventional formulation of cyclosporin A to he microemulsion formulation in stable renal transplant patients is both safe and well-tolerated.