The cause of hypospadias in the majority of patients is unknown. We examined the hypothesis that hypospadias might be explained by androgen receptor abnormalities in the atretic spongiosal tissue commonly known as chordee. We studied 10 patients with relatively severe hypospadias but with a predominantly male phenotype and no readily ascertained explanation for the defect, including no evidence of an abnormality in testosterone biosynthesis. Eight subjects had midshaft hypospadias and 2 had a penoscrotal meatus. All 10 patients had severe chordee. Serum concentrations of testosterone, and luteinizing and follicle-stimulating hormones were measured before human chorionic gonadotropin stimulation and a serum testosterone level was determined 24 hours after the last dose of a 5-day human chorionic gonadotropin stimulation (3,000 units per M.2 per day). Androgen receptor content and binding affinity were assayed in fibroblasts cultured from preputial skin and chordee tissue of patients and foreskin from normal male neonates. With the endogenous ligand dihydrotestosterone the mean number (maximum binding capacity) of androgen receptors was 1,013 fmol. per mg. deoxyribonucleic acid in preputial skin and 833 fmol. per mg. deoxyribonucleic acid in chordee tissue of patients, and 627 fmol. per mg. deoxyribonucleic acid in the foreskin of controls. With the nonmetabolizable, synthetic androgen methyltrienolone (R1881) the mean maximum binding capacity was 1,004, 722 and 758 fmol. per mg. deoxyribonucleic acid, respectively. Dihydrotestosterone receptor affinity (dissociation constant) was similar in preputial skin (0.20 nM.) and chordee tissue (0.21 nM.) from patients, and foreskin (0.29 nM.) from controls. Androgen receptor binding affinity of R1881 also was similar (0.30, 0.24 and 0.21 nM., respectively). Furthermore, the 5 alpha-reductase activity of preputial skin and chordee tissue of patients with hypospadias was similar to that of foreskin from normal neonates. In conclusion, isolated hypospadias in these subjects was not associated with androgen insensitivity of the spongiosal tissues on the basis of either decreased androgen receptor binding affinity, receptor number or conversion of testosterone to dihydrotestosterone.