MIS is a sexually dimorphic gonadal hormone that is tonically elevated in prepubertal males and low in females. We postulated that MIS determination would facilitate the evaluation of virilized children with nonpalpable gonads and would be predictive of testicular tissue. Thus, we measured MIS in 49 prepubertal children with nonpalpable gonads who subsequently were determined to have ovaries(5), absent(9) or normal(18) testes by abdominal exploration/orchiopexy, or abnormal testes [dysgenetic(6), ovotestes(3), torsion(1), and Leydig cell hypoplasia(1)] by pathology. MIS is detectable above the normal female range in all 31 patients with testicular tissue, including one with only histologic testicular elements following bilateral intrauterine torsion, but is absent in 8/9 patients with anorchia and 5 female pseudohermaphrodites. MIS is low in 8/11 patients with dysgenetic testicular tissue or ovotestes, and normal for age in 16/18 patients with normal appearing testes. The sensitivity and specificity of MIS for predicting testicular tissue is 93% and 100% respectively, the positive and negative predictive values are 100% and 88%. Therefore, MIS offers greater sensitivity and specificity for determining the presence of testicular tissue in prepubertal patients than either basal or hCG stimulated testosterone levels. In addition, MIS is able to distinguish between pathologically abnormal and grossly normal testes with a sensitivity of 82% and a specificity of 78%. We conclude that MIS is a clinically useful test in the initial evaluation of patients with virilized genitalia and nonpalpable gonads, particularly in deciding whether to perform a prolonged hCG stimulation test or to surgically explore the abdomen. Furthermore, MIS may be predictive of testicular pathology and potential endocrine function. Table

Table 1