Fasting primary bile acid conjugates were measured in 44 women by radioimmunoassay methods. Bile acid values were significantly greater in the 21 women who were in the first half of the menstrual cycle than in the 23 women in whom blood was sampled during the second half of the cycle. Similar measurements were made at weekly intervals after menstruation in five subjects; increased values were observed in the first week. It is concluded that serum bile acid values fluctuate during the menstrual cycle.

The measurement of serum bile acids has been advocated for the detection of liver disease. 1-3 Few studies have reported fasting serum bile acid values in small numbers of normal subjects. 45 So far the influence of factors such as age, drug therapy, and the menstrual cycle on fasting serum bile acids has remained largely unknown. Serum and biliary lipid composition is known to change during the course of the menstrual cycle. 6 We describe changes in the serum bile acid values which were observed during the menstrual cycle.