Interstitial cell carcinoma of the testis is a singularly rare steroid-producing cancer. Of the seven reported cases (1-7), urinary 17-ketosteroid (17-KS) excretion was high in the four cases in which it was measured. Abelson, Bulaschenko, Trommer, and Valdes-Dapena (7) fractionated the urinary 17-ketosteriods and corticoids in one recently reported case. There is, however, no comprehensive study of either the production of androgens or related steroids by this tumor. (testosterone) ; 17a-hydroxy-androst-4-en-3-one (epitestosterone); 3a-hydroxy-5,B-androstan-17-one (etiocholanolone); 3a-hydroxy-5a-androstan-17-one (androsterone); 3a,11,8-dihydroxy-51-androstan-3-one (11-hydroxyetiocholanolone); 3a-hydroxy-58-androstan-3,11-dione (ll-ketoetiocholanolone) ; 3a,11'B-dihydroxy-Sa-androstan-17-one (1l-hydroxy-androsterone); 3,B-hydroxy-androst-5-en-3-one (dehydroepiandrosterone, DHA); androst-4,en-3,17-dione (androstenedione); 3fi,16a-dihydroxy-5-androstan-17-one (16-hydroxy DHA); androst-5-en-3,8,17P-diol (androstenediol); pregn-5-en-3p8,20a-diol (pregnenediol); pregn-5-en-3fi,17a,20a-triol (pregnenetriol) ; 5,6-pregnan3a,20a-diol (pregnanediol); 5P-pregnan-3a,17a,20a-triol (pregnanetriol); 3a,17a-dihydroxy-5p8-pregnan-20-one (17-hydroxypregnanolone); 3a,17a,20a-trihydroxy-59-pregnan-l1-one (11-ketopregnanetriol); 5a-androst-16-en- 3,20-dione (cortisol) ; 3ac,11P,17a,21 -tetrahydroxy-5#9-pregnan-20-one (tetrahydrocortisol); 3a,17a,21-trihydroxy-5fi-pregnan-11,20-dione (tetrahydrocortisone) ; 3a, 11P,17a,21-tetrahydroxy-5a-pregnan-20-one (allotetrahydrocortisol) ; 3a,17a,21 -trihydroxy-5Sf-pregnan-20-one (tetrahydro substance S); 3-hydroxyestratrien-1,3,5 (10)-17-one (estrone); 1,3,5 (10-estratriene-3,17P-diol (estradiol); 1,3,5 (10)-estratriene-3,16a,17P-triol (estriol). 1700