From November, 1989, to October, 1991, 4544 neonates were born at our hospital. Neonatal ocular prophylaxis immediately after birth was used with 1% tetracycline ophthalmic ointment in 1156 neonates, 0.5% erythromycin ophthalmic ointment in 1163 neonates and 1% silver nitrate drops in 1082 neonates. No prophylaxis for neonatal conjunctivitis was given to 1143 neonates. A total of 302 infants (6.7%) developed conjunctivitis during the first 4 weeks of life. Between December, 1991, and January, 1992, 425 neonates were born at our hospital and all were given 0.5% erythromycin ophthalmic ointment twice in the first 24 hours after birth for ocular prophylaxis. Thirty-one (7.3%) infants developed conjunctivitis during the neonatal period. The incidence rates of neonatal chlamydial conjuctivitis in the tetracycline, erythromycin, silver nitrate, no prophylaxis and erythromycin twice groups were 1.3, 1.5, 1.7, 1.6 and 1.4%, respectively. We conclude that neonatal ocular prophylaxis with erythromycin (one or two doses) or tetracycline or silver nitrate does not significantly reduce the incidence of neonatal chlamydial conjunctivitis compared with that in those given no prophylaxis.