Partially purified human GH was subjected to chromatography on DEAE-cellulose to yield a preparation that lacked in vitro lipolytic activity in the rat epididymal fat pad even in the presence of dexamethasone. Release of both glycerol and FFA was examined after a 4-h incubation and was found to be unaffected by concentrations of GH as high as 0.1 mg/ml incubation medium. The lipolytic activity of the original partially purified GH was detected in an acidic fraction from the DEAE-cellulose chromatography. Similar results were obtained with bovine GH. Adipose tissue from rats fed Purina rat chow was more responsive to the lipolytic factor than tissue from rats fed a high sucrose, fat-free diet.