1. The effects of intravenous infusions of recombinant human insulin-like growth factor 1 and insulin on palmitate kinetics, lipolysis and on serum triacylglycerol were compared. Overnight-fasted normal subjects received high doses of insulin-like growth factor I (30 μgh −1 kg −1 ) and insulin (0.23 nmol h −1 kg −1 ; group 1), low doses of insulin-like growth factor I (5 μg h −1 kg −1 ) and insulin (0.04 nmol h −1 kg −1 ; group 2) or saline (control group). The doses of insulin-like growth factor I and insulin were equipotent with regard to increases in glucose uptake during 8 h euglycaemic clamping. 2. Whole-body palmitate flux (measured by continuous infusions of [2,2-D 2 ]palmitate) was lowered dose-dependently by 68% ± 6% during insulin-like growth factor I and by 82% ± 2% during insulin after 8 h of infusions of high doses (insulin-like growth factor I versus insulin; not significant). Plasma palmitate, glycerol and triacylglycerol concentrations had decreased to a similar extent at the end of the infusions of both peptides at either dose. 3. The present results demonstrate that insulin-like growth factor I and insulin infused at doses which result in identical increases in glucose uptake during euglycaemic clamping are equipotent inhibitors of lipolysis.