Growth hormone (GH) excess stimulates lipolysis, but its role in the hierarchy of lipolysis regulation is not clear. We studied whether pulsatile GH delivery is required for its lipolytic effect. With use of the pancreatic clamp, eight subjects were randomized to three protocols: protocol A, GH deficiency; protocol B, constant GH infusion; protocol C, pulsatile GH delivery (same total GH as protocol B). Pulsatile GH was given in four consecutive bursts, with symmetric peak width (60 min), amplitude of 10.7 (men) and 15 (women) ng.kg-1.min-1, and peak width at half-height of 15 min. Palmitate flux (PF) was measured at baseline and in the last hour of each study with [3H]palmitate. GH (ng/ml) decreased from approximately 3.5 to 2.0 in protocol A (P < 0.05), it remained between 3.2 and 4.0 in protocol B (P < 0.05), but in protocol C it fluctuated between approximately 2.7 and approximately 5.0 (P < 0.05). Palmitate concentration (in mumol/l) was approximately 150 at baseline; it did not change in protocols A and B (137 +/- 17 and 136 +/- 12, respectively) but increased to 198 +/- 16 (P < 0.05) in protocol C. PF (mumol.kg-1.min-1) was approximately 2.7 at baseline and did not change in protocol B (2.4 +/- 0.2); it decreased to 2.2 +/- 0.1 in protocol A (P < 0.05); it increased to 3.1 +/- 0.3 (P < 0.05) in protocol C. These experiments provide evidence that pulsatile secretion of GH is required for its lipolytic effect.