The effects of 6 months' treatment with recombinant human growth hormone (rhGH) on serum lipids and lipoproteins were assessed in 24 adult patients with GH deficiency in a double-blind, placebo-controlled trial. Compared with age-, weight-, and sex-matched controls, the patients had significantly higher serum concentrations of total cholesterol (P = .002), low-density lipoprotein (LDL) cholesterol (P < .001), apolipoprotein B ([apoB] P = .011), and triglyceride (P = .017), and lower concentrations of high-density lipoprotein (HDL) cholesterol (P < .001). The prevalence of elevated serum cholesterol, triglyceride, LDL cholesterol, and apo B levels was 39%, 26%, 39%, and 25%, respectively; 75% of patients had decreased concentrations of HDL cholesterol. Treatment with rhGH (0.07 U/kg daily) resulted in decreases in total cholesterol level (5.8 +/- 0.3 to 5.1 +/- 0.3 mmol.L-1 over 6 months; P = .01 compared with placebo), LDL cholesterol level (4.22 +/- 0.25 to 3.19 +/- 0.23 mmol.L-1; P = .0003), LDL:HDL cholesterol ratio (5.57 +/- 0.47 to 3.29 +/- 0.33; P = .03), apo B level (1.07 +/- 0.06 to 0.84 +/- 0.07 g.L-1; P = .003), and apo B: A-1 ratio (0.73 +/- 0.05 to 0.69 +/- 0.05; P = .01). HDL cholesterol and apo A-1 levels did not change following rhGH treatment. The changes in lipid and lipoprotein levels were not significantly related to changes in insulin, thyroid hormones, insulin-like growth factor-1 (IGF-1), or indices of adiposity.(ABSTRACT TRUNCATED AT 250 WORDS)