In view of a possible resistance to hormones as a cause of growth failure in renal insufficient children, a short-term study was performed to assess the effect of low-dose testosterone administration in boys with end-stage renal failure. Eight boys with a mean age of 11.4 +/- 1.2 years and a mean height deviation of -3.9 SD according to French standards received 50 mg/m2/day of a testosterone or placebo gel in a double-blind crossover fashion, each for a period of four weeks. Growth velocity was assessed by knemometry. The mean plasma testosterone levels rose from 0.16 +/- 0.06 ng/ml to 1.98 +/- 0.35 ng/ml during the testosterone treatment (p less than 0.01), whereas it remained low during the placebo treatment: 0.23 +/- 0.09 ng/ml versus 0.19 +/- 0.06 ng/ml before. The mean growth velocity rose from 0.27 +/- 0.07 mm/week during the control period to 0.50 +/- 0.03 mm/week during the testosterone treatment (p less than 0.05). Two groups of boys could be distinguished: the four boys of the first group whose initial growth velocity was below the mean growth velocity of a healthy control group, showed a significant improvements during the testosterone treatment (p less than 0.01). The growth velocity of the four boys of the second group whose initial growth velocity was normal did not improve during the testosterone treatment. These facts suggest that low dose testosterone can stimulate short-term growth of boys on regular hemodialysis when the basal growth velocity is low.