We have examined serum lipids and apoprotein levels and the formation of biliary sludge in 56 pregnant women. During pregnancy, 8 women showed biliary sludge which disappeared after delivery. Pregnant women with sludge had serum levels of total cholesterol, triglycerides, LDL-cholesterol and apo-B higher than women without sludge, although it was not statistically significant. Moreover, these women had serum levels of HDL-cholesterol and apoA1 significantly lower and LDL/HDL and apoB/apoA1 ratio significantly higher than the women without sludge. Thus, biliary sludge seems to be associated with serum lipid and apoprotein variations. Further investigations are required to clarify if these variations are also expressed in the bile.