Intrinsic growth rate and asymptotic body weight parameters were estimated for two laboratory and three field populations of the Wood mouse, Apodemus sylvaticus, using a logistic model fitted by an ordinary least squares method. The data upon which the growth equations were based were differences in body weight for individual animals between sampling occasions. Suckling mice in one of the laboratory studies suffered high mortalities and poor body growth which was related to disturbance to the mothers and their young during examination. Growth in weaned mice appeared normal and was compared with growth in autumn and winter populations of wild mice with poor and good natural seed supplies. Males tended to have higher growth rates, and to a lesser extent, higher body weight asymptotes than females in all groups. Growth rates were highest in the autumn field population with a good seed supply; differences between the other groups were less marked. These results are discussed and it is suggested that, despite the approximations inherent in the method, the method will be a useful tool for studying the the productivity of wild populations of small mammals.