This study shows that the two intestinal protozoa, Giardia lamblia, Balantidium coli in addition to Entamoeba histolytica are prevalent in the Ibadan population and are responsible for many of the non-bacterial diarrhoea seen in patients. A high seasonal prevalence of the intestinal protozoa in the dry months of the year was associated with the use of contaminated water. Both the high infection rates recorded in adults and children under five years old, and the high frequency of association involving Trichomonas hominis, Entamoeba histolytica and Giardia lamblia were discussed.