A "sinking" pre-beta lipoprotein was sought in a probability sample of 1854, 50--72-year-old men of Japanese ancestry in Honolulu by ultracentrifugation of plasma and electrophoresis of the bottom fraction (density greater than 1.006) in agarose. A definite electrophoretic band was found in 5.6% of the men and a trace band was found in 4.6% of them. The frequency of such a band increased with age and decreased with adiposity. The relative risk for coronary heart disease, based on prevalence cases was found to be 1.7 in men with a definite band, and 1.4 in those with a trace band, when compared to men without. This association could not be explained by the higher low density lipoprotein levels in men with trace or definite bands. These data are consistent with previous reports suggesting that the Lp antigen (for which a sinking pre-beta lipoprotein is probably an insensitive marker) is associated with coronary disease.