The aim of the study was to evaluate the in vitro activity of term human milk on the organisms of Ophthalmia neonatorum and was a prospective study of consecutive neonates with the organism. The study was undertaken in a special care baby unit/lying-in ward in Benin City, Nigeria, and consisted of 22 neonates with ophthalmia neonatorum. Bacterial organisms grown on blood agar, were obtained from eye swabs of neonates with ophthalmia neonatorum. Inoculated isolates were incubated with known antibiotic discs, term colostrum, and mature milk. Bacteria were isolated in 77 per cent (17/22) of the neonatal eye swabs, 59 per cent of which were Staphylococcus aureus and 41 per cent coliform organisms. Sensitivity of Staphylococcus aureus to gentamicin was 100 per cent and for coliform organisms 42 per cent. The sensitivity of Staphylococcus aureus to term colostrum was 50 per cent and to mature milk 0. Coliform organisms had a sensitivity of 57 per cent to colostrum and 28 per cent to mature milk. The zone of inhibition of colostrum against Staphylococcus aureus and coliform organisms was between 3 and 5 mm, while for mature milk, there was partial or no inhibition, respectively, to coliform organisms and Staphylococcus aureus. The mean duration of inhibition was 6 hours for colostrum and 3 hours for mature milk. Colostrum has about half the in vitro inhibitory activity of gentamicin (recommended as a first line topical agent, based on the bacteriological sensitivity of this study) against Staphylococcus aureus and coliform organisms. The inhibitory activity of colostrum is > or = 50 per cent against Staphylococcus aureus and coliform organisms for a mean duration of 6 hours. Mature milk had no inhibitory activity against Staphylococcus aureus and only 28 per cent inhibition, for a mean duration of 3 hours to coliform organisms.