Untreated acromegaly is associated with an increased cardiovascular morbidity and mortality. The contribution of altered lipid metabolism remains unclear. We investigated the relationship between serum apolipoprotein(a) (apo(a)) and growth hormone (GH) levels in 15 patients with acromegaly before and during treatment with octreotide, a long-acting somatostatin analogue, 288-600 micrograms/day s.c., for 6 months. Before treatment serum apo(a) was significantly elevated in acromegalic patients (geometric mean being 323 U/l vs. 142 U/l in controls (n = 92; P < 0.01)). Octreotide treatment resulted in significant reductions in serum apo(a) concentration (F = 7.22; P < 0.01; geometric mean being 232 U/l and 248 U/l at 3 months and 6 months respectively) and apo(a) concentrations on treatment were not significantly different from control values. There were significant reductions in serum GH (F = 7.30; P < 0.01), insulin growth factor 1 (IGF1) (F = 31.4, P < 0.001) and insulin (F = 4.57; P < 0.05) concentrations. Plasma glycosylated haemoglobin levels were unchanged. Apo(a) levels correlated with serum GH (r = 0.450; P < 0.01) but showed no correlation with basal insulin concentrations. Serum HDL cholesterol increased on treatment (F = 4.29; P < 0.05). Triglycerides were reduced only in the 12 patients without diabetes mellitus (F = 4.75; P < 0.05). No significant change in LDL cholesterol occurred. Our findings suggest that apo(a) may constitute another cardiovascular risk factor in untreated acromegaly and that GH may be involved in the regulation of circulating apo(a) concentration.