Previous work in this laboratory indicated that sulfur-substituted fatty acid analogues, 1.10-bis(carboxymethylthio)decane and alkylthioacetic acid, both non-beta-oxidizable compounds, and the beta-oxidizable alkylthiopropionic acid (1) caused, to different extents, dose-related hepatomegaly and proliferation of peroxisomes and enhanced peroxisomal fatty acid beta-oxidation. In the present study, treatment of normolipidemic rats with alkylthioacetic acid resulted in a dose- and time-dependent decrease in serum cholesterol and serum and liver triglycerides to an extent comparable to that of the 3-thiadicarboxylic acid. At hypolipidemic doses, alkylthioacetic acid caused no hepatomegaly, did not significantly alter peroxisome morphology, and only marginally affected peroxisomal beta-oxidation activity. Only at the highest, nonpharmacological doses of alkylthioacetic acid were these hepatic parameters increased, although to a lesser extent than by the 3-thiadicarboxylic acid. Hence, on the basis of dose- and time-related studies of the two compounds, data indicate that the hypotriglyceridemia and hypocholesterolemia were dissociated from induction of peroxisomal beta-oxidation and peroxisome proliferation. Palmitic acid and hexadecanedioic acid, both beta-oxidizable fatty acids, only marginally affected the serum and liver parameters. The beta-oxidizable fatty acid analogue, alkylthiopropionic acid lowered the serum triglycerides in normolipidemic rats. In contrast to the 3-thiadicarboxylic acid and alkylthioacetic acid, alkylthiopropionic acid treatment at hypolipidemic doses caused accumulation of triglycerides in the liver.