Two 3-year prospective studies from 1982-1984 and 1986-1988 in Tanzania identified 189 children with corneal ulceration, of whom 92 (48.7%) were due to herpes simplex keratitis. In 1982-1984 herpes simplex keratitis was responsible for 35.5% of corneal ulcers (38 of 107), compared with 65.8% (54 of 82) in 1986-1988 (P = 0.00006). It is postulated that the increase in corneal ulceration due to herpes simplex keratitis can be attributed to an increase in the incidence and severity of malaria infection.