The intensity of growth of Sorex araneus L. and Clethrionomys glareolus Schreb. in the Oulu district of Finland is studied as a function of age and seasonal rhythm, and compared with the results of growth-rate measurements of Sorex araneus L., Clethrionomys rufocanus Sund. and Clethrionomys rutilus Pall. in Kirkenes, Norway. It is assumed that the postnatal development of the Common shrew with its growth and regression phases is to some extent controlled by an endogenous seasonal rhythm. The growth of the voles is not as clearly controlled by these rhythms as that of the Common shrew although the growth of the Bank vole and Northern red-backed vole is obviously considerably retarded in autumn and in winter.