To investigate the effects of renal transplantation (Rtx) on the nutritional status, muscle composition and the plasma and muscle free amino acid (AA) pattern, three groups of altogether 30 renal transplant patients (group I n = 10; 46 +/- 14 [SD] days after Trx), (group II n = 10; 13 +/- 2 months after Rtx) and (group III n = 10; 9 +/- 2 years after Rtx) underwent anthropometric measurements, blood sampling and percutaneous muscle biopsy. The immunosuppressive therapy consisted of prednisolone, azathioprine and cyclosporine-A. The results were compared with data from age-matched healthy subjects. Renal function was impaired in groups I, II and III. Serum albumin was decreased in groups I and II. The patients of group II had an increased percentage of body fat, triceps and subscapular skin folds and total sum of skinfolds. In group I the ratio alkaline-soluble protein (ASP) to DNA, which is a sensitive index of protein depletion on the cellular level, was decreased. Muscle magnesium content was decreased whereas the muscle DNA, sodium and chloride contents were increased. The mean plasma concentration of most essential AA (EAA) was essentially normal except phenylalanine which was increased in groups I and II.(ABSTRACT TRUNCATED AT 250 WORDS)