The metabolism of fenfluramine in man results in the excretion of unchanged fenfluramine, deethylated fenfluramine, and m‐trifluoromethylhippuric acid. Methods are described for the determinations of these three compounds and the total metabolites in urine by GLC. The m‐trifluoromethylhippuric acid accounts for 66 to 93 percent of the dose and 79 to 100 percent of the dose may be accounted for as these three metabolites. Copyright © 1968 Wiley‐Liss, Inc., A Wiley Company