The aim of this prospective and randomized study was to determine whether misoprostol, an analogue of PGE1, could decrease the incidence and the number of rejection episodes and could improve the renal function over a 12-month follow-up, when given at 400 micrograms/day for 12 months in renal transplant patients. Given the known side-effects and the additive cost of misoprostol, a benefit of the therapy should be a decrease of at least 50% in the incidence of rejection episodes in the treated group. Therefore, 60 consecutive renal transplant patients were randomized to receive misoprostol or to receive aluminium and magnesium hydroxide. Patients received steroids, azathioprine, antithymocyte globulins, and cyclosporin A (CsA). CsA was randomly started on day 0 or on day 8. At 12 months, no difference in the incidence of rejection episodes was observed: 63.3% in the 30 patients of the misoprostol + group versus 70.0% in the misoprostol-group (P = 0.558 Mantel-Cox). The renal function, assessed by plasma creatinine, inulin, and para-aminohippuric acid clearances, was not significantly different between misoprostol + and misoprostol-groups. No episode of CsA nephrotoxicity was observed in any patient of group one or group two. At 12 months, the mean dosage of CsA was 4.9 +/- 0.28 mg/kg/day in the misoprostol + group versus 4.52 +/- 0.23 mg/kg/day in the misoprostol-group and the trough level was not significantly different between the two groups. The graft survival rate at 12 months was 86.7% in the Misoprostol + group and 83.33% in the misoprostol-group.(ABSTRACT TRUNCATED AT 250 WORDS)