Prompted by the finding that the radiological incidence of small bowel ascariasis in the patient with gastriccarcinoma was unexpectedly lower than the incidence in the normal population, a clinical study was performed toinvestigate possible relationship between gastric carcinoma and intestinal ascariasis. As a preliminary survey, wereviewed the radiological incidence of ascariasis in a total of 2,446 cases of upper GI series performed at theDepartment of Radiology, St. Mary's Hospital, Catholoic Medical College. These included 1,573 normal subjects, 146gastric carcinoma patients, 100 benign gastric ulcer and 249 duodenal ulcer patients and 378 other upper GIdiseases. Following the preliminary study, a more accurate parasitologic study was conducted in another 578 normalsubjects and 51 gastric carcinoma patients. The radiological incidences of ascariasis in normal subjects andgastric carcinoma patients were 15.1% and 28.1%, respectively. The incidence of overall helminthiasis includingascaris lumbricoides, trichocephalus trichiurus and trichostronglyoides orientalis in normal subjects of thepresent series was 73.5%. This figure is virtually the same wtih 69.1% of the general population incidencereported by Kim et al. (1971), but the incidence in gastric carcinoma patient is, however, reversed as far asascariasis is concerned. Thus, the incidence of ascariasis of gastric carcinoma patients was much lower than thatof normal subjects (9.8% vs 19.4%). From the present observation, it is postulated that there can be some possibleantagonistic relationship between evolution of gastric carcinoma and small bowel infestation of ascarislumbricoides.