Genomic hybridization analysis has been used to investigate allelic frequencies of the genes coding for the four major apoproteins of high density lipoprotein (HDL); apoproteins AI, AII, CII and CIII, in a group of Caucasian subjects with primary gout. An uncommon allelic variant of the apoprotein CIII gene (the S2 allele) was significantly more common among the patients with gout (9/48, 19%) than among normouricaemic controls who were either randomly selected (1/41, 2%, P = 0.03) or normotriglyceidaemic (0/33, 0%, P = 0.013). Approximately 46% (22/48) of the subjects with gout were hypertriglyceridaemic (with a serum triglyceride greater than 2.1 mmol/l). Of the 22 patients in this subgroup, 5 (23%) had the uncommon S1S2 genotype, which was also a significantly greater proportion than among the normotriglyceridaemic controls (P = 0.015). These data suggest that the hypertriglyceridaemia associated with primary gout may have a genetic basis. In contrast, we found no differences in the frequencies of restriction fragment length polymorphisms of the genes for apoproteins AI, AII and CII.