Alterations of plasma lipids and lipoproteins occur during mammalian pregnancy and reproduction. This study investigated the effects of dietary fatty acids on plasma lipid and lipoprotein alterations during canine gestation, lactation, and the neonatal period. Four diets containing varying amounts of alpha-linolenic acid relative to marine-based (n-3) long-chain fatty acids were studied and fed to dogs from the time of estrus, and throughout pregnancy and lactation. In addition, puppies born to these dams suckled and were weaned using the same diets their mothers had been fed. Plasma cholesterol (total, free, and esterified fractions) and triglycerides were determined at selected time points and lipoprotein fractions were characterized in both mothers and offspring. During gestation, plasma total cholesterol concentrations were depressed early on, then increased in the later stages independently of diet. Both beta- and alpha2-migrating lipoproteins also increased during these times. Lactation was also characterized by lower lipid and lipoprotein amounts compared with the nonpregnant state. In puppies, total plasma and beta-lipoprotein cholesterol were elevated at 4 and 10 d of age. Diet effects included cholesterol, triglyceride, and lipoprotein lowering with increased amounts of marine (n-3) fatty acids in all life stages investigated. The increase in beta-lipoprotein cholesterol in puppies during wk 1 of life is consistent with an earlier report of increased canine apoprotein B,E receptor activities in immature dogs compared with undetectable activities in mature animals in which the HDL fractions become even more predominant in this species.