A newly recognized protozoan human parasite, Cyclospora spp. has been incriminated as the cause of prolonged diarrhoea. It has been isolated from children, immunocompetent and immunocompromised adults. One hundred and thirty immunocompetent patients, 80 children and 50 adults; their illness was characterized by prolonged watery diarrhoea, were enrolled in this study. Stool sediments were examined as wet mounts and stained by both, modified Ziehl-Neelsen and aniline carbol methyl violet stains. The protozoan pathogen was identified as spherical bodies measuring 9-10 microns in diameter in about 9% and 10% in both children and adult groups respectively. The mean duration of illness was 28 +/- 8 and 37 +/- 12 days and the frequency of stool motions was > 5/day with normal mucosal pattern on colonoscopic studies for adults group. It is concluded from the present study that cyclosporiosis is quite similar to cryptosporidiosis and both oocysts have the affinty to acid fast stain so the present recommendations for all laboratories screening stool for cryptosporidia should measure the oocyst to distinguish between these different parasites and there is obviously a great deal more to learn about this emerging protozoon.