One hundred and thirty-seven cases of stomach cancer given fluoropyrimidines (UFT: 66 cases, Tegafur: 58 cases, 5-FU: 13 cases) after gastrectomy as the adjuvant chemotherapy were examined as to appearance of macrocytic anemia. The mean corpuscular volume (MCV) gradually elevated in all cases but seven after administration. Macrocytic anemia, defined by the elevation over 20% compared with both pre-operative and pre-administrative values of MCV, was developed 30.3% in UFT group, 8.6% in tegafur group and 30.8% in 5-FU group. The incidence was statistically higher in UFT group (p less than 0.01) and 5-FU group (p less than 0.05) than in tegafur group. The cause was attributed to fluoropyrimidine administration because the serum folate and vitamin B12 levels remained normal and the value of MCV normalized after cessation of administration. Each total dose to induce macrocytic anemia was potentially about 70g in UFT. 100g in tegafur and 30 g in 5-FU. In conclusion, periodical hematological examination is necessary for the patients given fluoropyrimidine preparations.