Growth hormone (GH) insufficiency was demonstrated in a patient with methylmalonic aciduria. GH administration at 14-21 U/m2 per week accelerated linear growth, stimulated lipolysis, and produced clinical improvement and reduced urinary methylmalonate excretion. The clinical and metabolic benefits were lost as the dose of GH was increased to 28 U/m2 per week. CONCLUSION. The use of GH in other patients with methylmalonic aciduria (and other disorders of intermediary metabolism demonstrating similar clinical and metabolic features) warrants further study.