CONTEXT: The ability of growth hormone (GH) to stimulate lipolysis and to cause insulin resistance in skeletal muscle may be causally linked, but the mechanisms remain obscure. INTERVENTIONS: We investigated the impact of GH on the turnover of FFA and VLDL-TG, intramuscular triglyceride content (IMTG) and insulin sensitivity (euglycemic clamp) in 9 healthy men in a randomized double-blind placebo-controlled crossover study after 8 days treatment with A) Placebo + Placebo, B) GH (2 mg daily) + Placebo, and C): GH (2 mg daily) + Acipimox (250 mg x 3 daily). RESULTS: In the basal state GH (B) increased FFA levels (P < 0.05), palmitate turnover (P < 0.05), and lipid oxidation (P = 0.05), but VLDL-TG kinetics was unaffected. Administration of acipimox (C) suppressed basal lipolysis but did not influence VLDL-TG kinetics. In the basal state IMTG content increased after GH (B) (P = 0.03). Insulin resistance was induced by GH irrespective of concomitant acipimox (P < 0.001). The turnover of FFA and VLDL-TG was suppressed by hyperinsulinemia during placebo and GH, whereas co-administration of acipimox induced a rebound increase FFA turnover and VLDL-TG clearance. CONCLUSIONS: 1) These results show that GH-induced insulin resistance is associated with increased IMTG and unaltered VLDL- TG kinetics, 2) we hypothesize that fat oxidation in muscle tissue is an important primary effect of GH and that circulating FFA rather than VLDL-TG constitute the major source for this process, 3) the role of IMTG in the development of GH-induced insulin resistance merits future research.