It has been known for over 25 yr that feces from rats infected with the tapeworm Hymenolepis diminuta are more attractive to tenebrionid beetle intermediate hosts than feces from uninfected rats. Although it has been demonstrated that a volatile chemical (or chemicals) in infected rat feces attracts the intermediate host Tribolium confusum, the volatile chemical(s) have never been identified. This study aimed to identify and compare the volatiles in the feces of rats before and after infection with H. diminuta. Four 8-wk-old female Sprague Dawley rats were infected with H. diminuta. Fecal samples pre- and postinfection were collected, and volatiles were trapped by vacuum on a polymer adsorbent and identified with gas chromatography–mass spectrometry analysis. Limonene was detected in preinfection but not postinfection feces. Five carboxylic acids were isolated only from postinfection feces. Butanoic acid was found in the greatest relative amount, but also 3-methylbutanoic acid, 2-methylbutanoic acid, pentanoic acid, and hexanoic acid were found. This is the first report identifying the volatiles found in the feces of rats infected with H. diminuta.