The relations between serum lipids, ABO and Lewis blood groups and alkaline phosphatase isozymes were studied in a series of 291 Swedish military conscripts. The level of esterified cholesterol was significantly higher in individuals of blood group A compared to those of blood groups AB and O. The correlation between blood groups and esterified cholesterol was most likely not mediated through intestinal alkaline phosphatase, since no significant correlations were found between the levels of serum lipids and that of the intestinal alkaline phosphatase isozyme. The levels of all serum lipids examined and particularly that of the triglycerides showed a significant negative correlation with the level of the liver alkaline phosphatase isozyme.