The ultracentrifugal flotation patterns in 1.2 g/ml solvent and ultracentrifugal gradient distribution of high density lipoproteins (HDL) from the primates--human, apes and monkeys--were determined, with emphasis on the gorilla species of apes and rhesus monkeys. Diets for non-human primates were commercial chow, which is low in cholesterol. Molecular weights and protein, cholesterol, phospholipid and triglyceride compositions of various density fractions were determined on human, gorilla and rhesus HDL. The HDL2/HDL3 ratio was determined from the two peaks observed upon flotation in high salt in the analytical ultracentrifuge. The HDL2 of all three species of apes--gorillas (Gorilla gorilla), chimpanzees (Pan troglodytes) and orangutans (Pongo pygmaeus)--was always greater than HDL3, while that of all six species of Old World monkeys--Rhesus (Macaca mulatta), sooty mangabeys (Cercocebus atys), cynomolgus (Macaca fascicularis), stumptails, (Macaca arctoides) patas (Erythrocebus patas) and African greens (Cercopithecus aethiops)--was less. In addition, the HDL3 concentration in five gorillas was about 15 mg/dl as cholesterol while the HDL2 concentration was 92 mg/dl, much lower and higher, respectively, than humans. HDL2 of gorillas was similar in density and molecular weight to that of humans. The distribution of densities in gorilla HDL was predominantly in HDL2, while rhesus HDL usually, but not always, was unimodal, having a density distribution similar in heterogeneity to human HDL3, but somewhat less dense (peaking at 1.109 vs. 1.129 g/ml). The molecular weight of rhesus HDL was about the same as human HDL3 in all three density subfractions and at the peak density.(ABSTRACT TRUNCATED AT 250 WORDS)