Summary: In the 1934 epidemic of poliomyelitis in Denmark, we have collected 1118 cases in which the blood group of the patients was recorded. For comparison we offer nearly 20,000 cases of blood groups in the state of Denmark. There is no significant difference in the percentage of polio cases in each blood group as compared with the general population. The series which includes paralytic cases of known blood group (47 cases) is too small for comparison, although the data are presented. From these data we conclude that there is no especial susceptibility or resistance to poliomyelitis attack, which may be related to the blood group of the patient, in the cases occurring in the epidemic under discussion.