Effects of cyclosporine A on kidneys of rats and the effects of carvedilol or BL-443 on kidneys of rats with cyclosporine nephropathy were studied. Male rats (Wistar) were divided into four groups (n = 7). Three groups of rats were treated in single oral daily doses of 45 mg cyclosporine A/kg body weight to cause cyclosporine nephropathy. Two of the treated groups were then medicated either with carvedilol or BL-443 in single daily doses of 10 mg/kg b.w., and 1 ml doses of saline were given daily i.p. to the third group of rats. Animals were treated and medicated for 17 days. The rats of intact group had no treatment and medication. L-lactate dehydrogenase isoenzymes LD(1-4) in the kidney extracts were determined by polyacrylamide gel clectrophoresis. Significant differences of LD(1-4) pattern in kidneys between intact rats and each of the three groups of rats with cyclosporine nephropathy were found by F-test and t-test (p < 0.05). Treatment with cyclosporine A affected the LD(1-4) pattern in kidneys. On the other hand, no significant differences of LD(1-4) pattern in kidneys between rats with non-treated cyclosporine nephropathy and rats with cyclosporine nephropathy medicated with carvedilol or BL-443 were found.