Abstract
1. A method of trapping small mammals has been described and Apodemus sylvaticus, Clethrionomys glareolus, Microtus agrestis and Sorex araneus were captured. The method of trapping has been discussed.2. A survey of the endoparasites found in the four host species has been produced. The two more common hosts and four of their parasites have been chosen for more detailed study.3. The infection levels of the parasites in the two hosts have been calculated and compared with other published data.This work was carried out during the tenure of a Department of Scientific and Industrial Research Studentship. My thanks are due to Dr H. D. Crofton for his very helpful supervision and criticism and to Professor J. E. Harris, F.R.S., in whose department this work was done, for the facilities provided.