Anthonisen. P. & Riis, P. 1971. Eosinophilic Granulocytes in the Rectal Mucus of Patients with Ulcerative Colitis and Crohn's Disease of the Ileum and Colon. Scarrd. J . Gusrroerir. 6 , 731-734.The frequent presence of inflammatory eosinophilia in ulcerative colitis, compared with other inflammatory states such as Crohn's disease. has previously been described by us. This investigation is a controlled study of the observation. 359 patients with ulcerative colitis and 36 patients with Crohn's disease of the small and large bowel, both fulfilling the department's diagnostic criteria of the two diseases, were included in the study. Cytological imprints of the rectal mucus by first diagnostic contact were blindly classified according to presence or absence of eosinophilia. Inflammatory cells \\ere present in 351 patients with ulcerative colitis and 26 with Crohn's disease. Eosinophilia was detected in 248 (70%) and 4 (approx. 15Yc) respectively. The difference of proportions is highly significant. The demonstration of cytological eosinophilia in a non-glucocorticoid-treated patient thus makes a diagnosis of ulcerative colitis more likely than one o f Crohn's disease.