Pituitary and gonadal function was studied in 18 boys from the rural Nile Valley who had retarded growth and delayed sexual maturation. A group of 8 boys with normal somatic and sexual development for this area was also studied. Both groups had a variety of parasites, hepatosplenomegaly, and iron and zinc deficiencies. The “retarded” patients had lower plasma LH levels than the “normal” boys, suggesting that their delayed puberty was due to hypogonadotropism rather than to Leydig cell failure. However, in both “normal” and “retarded” groups only 75% of the subjects had a normal increment in plasma testosterone during HCG treatment. Both groups were insulin sensitive and, although growth hormone was detectable in all subjects, only 4 of 18 “retarded” and 4 of 8 “normal” boys had an appropriate rise in plasma growth hormone during insulin hypoglycemia. The socioeconomic conditions, associated growth retardation and delayed puberty were discussed. It was concluded that it is not possible to attribute the delayed development of the boys in the rural Nile Valley solely to zinc deficiency.