Three patients with idiopathic ulcerative colitis and infection of Entamoeba histolytica were reviewed. They represented three different relationships between the two conditions, vis asymptomatic carrier, coexisting infection and superinfection causing exacerbation of colitis. A two-way relationship between amoebic colitis and ulcerative colitis has been discussed and the possible mechanisms in the literature have been reviewed. In patients with a short history of diarrhoea and in tropical countries where amoebic infection is endemic, it is important to role out amoebic colitis before commencing steroid therapy for inflammatory disease.