Cholesteryl ester and phospholipid transfer activities were determined in plasmas from 14 vertebrates, and lipid transfer values were analyzed in the light of the known atherogenesis susceptibility of studied species. Whereas cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activities among vertebrate species were only measured in lipoprotein-deficient fractions in previous studies, both endogenous lipoprotein-dependent and endogenous lipoprotein-independent assays were used in the present work. In agreement with previous studies, a few species (chicken, man, rabbit and trout) displayed substantial CETP activity, whereas CETP activity was not detectable in other species (cow, dog, horse, mouse, pig, and rat). Additional species that were not studied before, i.e. cat, goat, and sheep, were shown to be deficient in plasma cholesteryl ester transfer activity, while duck was shown to constitute a new member of the high activity group. Unlike CETP activity, PLTP activity was detected in plasmas from all studied species, most of them being assayed here for the first time (cat, chicken, cow, duck, goat, horse, sheep, and trout). While dog, trout, mouse, and pig displayed the highest phospholipid transfer activity levels, the remarkable preservation of facilitated phospholipid transfers in plasma from all vertebrates might indicate an essential role of PLTP in vivo. Interestingly, animals with well-documented atherogenesis susceptibility (chicken, pig, rabbit, and man) displayed significantly higher mean CETP activity, but lower mean PLTP activity than known 'resistant' animals (cat, dog, mouse, and rat). In conclusion, the present study revealed marked differences in plasma lipid transfer activities between vertebrate species, and interspecies comparisons indicated that both CETP and PLTP may constitute two determinants of the atherogenicity of the plasma lipoprotein profile.