Previous results suggested that strains C57BL/6J and C3H/HeJ differed in a single gene for atherosclerosis susceptibility, called Ath-1. Based on data from recombinant inbred strains Ath-1 was tentatively assigned to chromosome 1 linked to Alp-2. In this report, a cross between C57BL/6 and C3H/HeJ was carried out in order to test whether the tentative map position was correct. Parental strains and F1 and F2 progeny were examined. Susceptible alleles of Ath-1, found in C57BL/6, are associated with relatively low levels of high-density lipoprotein (HDL)-cholesterol in animals fed an atherogenic diet; resistant alleles of Ath-1 are associated with relatively high levels of HDL-cholesterol. F1 progeny have HDL levels that are intermediate between these of the two parental strains. Among the F2 progeny, Alp-2 and Ath-1 cosegregated, providing confirmatory evidence that Ath-1 is linked to Alp-2 on chromosome 1. Three mice recombinant for Alp-2 and Ath-1 were found among the 60 chromosomes tested, giving an estimated map distance between these two genes of 5.0 +/- 2.8 (SE) cM. The phenotypic characteristics of Ath-1 resemble a genetic trait in humans, hyperalphalipoproteinemia, which is characterized by elevated levels of HDL-cholesterol, reduced risk of heart disease, and increased longevity.