5-Nucleotidase (5-Nase) was determined in the serum of 67 Egyptian Children: 15 cases as a control group, 10 cases with infantile rickets, 8 cases with the so-called physiological jaundice of the newborn, 4 cases with rhesus incompatibility, and 30 cases with infective hepatits. In rachitic cases and in cases with icterus neonatorum, 5-Nase was not increased, while in cases with infective hepatitis it showed a statistically significant elevation when compared with the control group.