Intestinal parasites are the important etiological agents of water and food related diarrhea cases which are frequently seen during summer/early autumn seasons in developing countries. This point prevelance study was aimed to determine the protozoal antigen positivity rate in diarrhea cases admitted to the emergency service in one single day. A total of 198 diarrheal patients (90 male, 108 female; age range: 1-82 years, mean age: 29 years) who were admitted to the emergency service of Ankara Training and Research Hospital were included in the study. Macroscopic and direct microscopic examinations were performed for the stool samples of patients, and the samples which yielded pathological microscopic findings (e.g. presence of leukocytes, erythrocytes, and trophozoits) were investigated in terms of Entamoeba histolytica adhesin antigen, Giardia intestinalis cyst antigen and Cryptosporidium oocyst antigen by commercial ELISA kits (Techlab, USA). Macroscopic examination of the stool samples revealed that 60 (30%) of them had blood and mucous, 137 (69%) were watery and one sample had normal appearance. Pathologic results were obtained for 96 (48.5%) of the samples by microscopic examination: 36 (37.5%) revealed erythrocytes, 90 (93.7%) had leukocytes and 3 (1.5%) had G.intestinalis trophozoites. Since Shigella spp. were cultured in two of these 96 samples, these two cases were omitted from the study and 94 samples were investigated by ELISA assays. G.intestinalis was detected in 13 (13.8%) and E.histolytica in 2 (2.1%) samples while Cryptosporidium antigen was not detected in any of the samples by the ELISA assays. It was concluded that ELISA antigen assays were rapid and cost-effective methods for the determination of the causative agent in cases of diarrhea.