Objective: to assess the 24-h endogenous secretory growth hormone (GH) profile and serum insulin-like growth factor-I (IGF-I) response to exogenous recombinant human growth hormone (rhGH) in a patient with Werner's syndrome. Design: blood sampling every 20 min for 24 h followed by three daily injections of growth hormone. Setting: General Clinical Research Center. Patients: single patient with Werner's syndrome. Measurements: serum GH and IGF-I. Results: Growth hormone pulses were absent during the 24-h monitoring period. Likewise, integrated GH concentrations were very low at 0.25 μ min/mL, and no peaks occurred after sleep onset. Following single daily administration of rhGH, serum GH and IGF-1 rose. Conclusions: our findings support previous but less extensive studies suggesting patients with Werner's syndrome have reduced growth hormone levels. Preliminary investigations using rhGH in patients with Werner's syndrome should be considered.