We examined the relationship between maternal smoking during pregnancy and serum lipid, lipoprotein and apolipoprotein levels in newborns. Serum concentrations of total cholesterol, triglyceride, high density lipoprotein cholesterol, low density lipoprotein cholesterol, apolipoprotein A-1, apolipoprotein B and lipoprotein (a) were assesed in blood samples from 38 mothers who were smokers and their newborns obtained at delivery and compared to blood sample from 42 nonsmokers and their newborns. As compared with newborns of nonsmoker mothers, newborns of smoker mothers showed a lower mean level of high density lipoprotein cholesterol (21 versus 26 mg/dl, p < 0.01), a higher total cholesterol to high density lipoprotein cholesterol (4.7 versus 3.7, p < 0.01), a higher low density Lipoprotein cholesterol to high density lipoprotein cholesterol ratios (3.2 versus 2.3, p < 0.05), a lower mean level of apolipoprotein A-1 (105 versus 129 mg/dl, P < 0.01) and a higher apolipoprotein B to apolipoprotein A-1 ratio (0.44 versus 0.3, P < 0.01). These paremeters were also different between smoker and nonsmoker mothers. There were no significant differences in TC, TG, LDL-C, Apo B and Lp (a) values between the two newborn groups. These data suggest that maternal smoking during pregnancy markedly affects lipid metabolism in the fetus.