7α-hydroxycholestenone, a metabolite in bile acid synthesis, is derived from 7a-hydroxycholesterol and can be further metabolized to 7a,12a,-dihydroxycholest-4-en-3-one. Analysis of 7a-Hydroxycholestene-3-one (HCO) in serum may serve as a novel, simple, and sensitive method for the detection of bile acid malabsorption in patients with chronic diarrhea of unknown origin.