During a 10-year period 65 children and adolescents with ambiguous genitalia 
from the Dominican Republic, not known through kindred studies of 5 
alpha-reductase deficiency, were evaluated. Plasma androgen determinations were 
performed before and/or after Leydig cell stimulation of the testes with human 
chorionic gonadotropin. Of the children there were 24 female 
pseudohermaphrodites, 21 of whom had 21-hydroxylase deficiency, 1 true 
hermaphrodite and 40 (62 per cent) male pseudohermaphrodites. One child had a 
human chorionic gonadotropin response suggestive of 17-20 desmolase deficiency, 
and on further evaluation he also had partial deficiencies of the enzymes 
21-hydroxylase and 17 alpha-hydroxylase. Five subjects had a female phenotype 
and subnormal androgen responses to human chorionic gonadotropin. In 5 of 33 
male pseudohermaphrodites with a normal testosterone response to human chorionic 
gonadotropin 5 alpha-reductase deficiency was suspected by elevated plasma 
testosterone/dihydrotestosterone ratios before and/or after human chorionic 
gonadotropin stimulation. The diagnosis of 5 alpha-reductase deficiency was 
confirmed by elevated 5 beta/5 alpha urinary C19 and C21 steroid metabolite 
ratios. One subject with 5 alpha-reductase deficiency was traced to the original 
Dominican kindred of 38 affected subjects. Pedigree analysis of another proband 
revealed 3 additional affected relatives. Four subjects with a normal 
testosterone response to human chorionic gonadotropin had XO/XY gonadal 
dysgenesis. There were 25 male pseudohermaphrodites with normal plasma 
testosterone and dihydrotestosterone responses to human chorionic gonadotropin, 
who were not diagnosed by this methodology. This study reveals that 5 
alpha-reductase deficiency occurs with a frequency of 13 per cent as a cause of 
male pseudohermaphroditism in the Dominican Republic with approximately the same 
frequency as XO/XY gonadal dysgenesis. Unlike female pseudohermaphrodites, the 
majority of male subjects with pseudohermaphroditism remain unclassified by 
these techniques.