The antimicrobial activities of Moringa oleifera leaves, roots, bark and seeds were investigated in vitro against bacteria, yeast, dermatophytes and helminths pathogenic to man. By a disk-diffusion method, it was demonstrated that the fresh leaf juice and aqueous extracts from the seeds inhibit the growth of Pseudomonas aeruginosa and Staphylococcus aureus and that extraction temperatures above 56 degrees C inhibited this activity. No activity was demonstrated against four other pathogenic Gram-positive and Gram-negative bacteria and Candida albicans. By a dilution method, no activity was demonstrated against six pathogenic dermatophytes. A method was standardized for studying the effect of aqueous extracts on Ascaris lumbricoides eggs, but no activity was exhibited by any part of the tree in contrast to Chenopodium ambrosioides leaf extracts.