Three patients with nephropathic cystinosis and chronic renal disease, treated since early childhood with orally administered cysteamine, had an accelerated rate of rise of serum creatinine values after receiving recombinant human growth hormone. During 18 to 24 months of growth hormone treatment, each patient had a twofold to fourfold increase in growth velocity. The slope of the plot of reciprocal serum creatinine values versus age for each patient after growth hormone treatment was significantly steeper than the pretreatment slope. Growth hormone treatment had no effect on the rate of change of the uncorrected 24-hour renal creatinine clearance. We conclude that these patients gained body size but failed to compensate for their increased creatinine production with an increase in glomerular filtration rate. The result was an accelerated rate of rise of their serum creatinine values, hastening renal transplantation in one patient and the anticipated need for transplantation in another.