Sample frequency distributions are given of height and weight measurements of London elementary school children made during the period 1935–8. In addition these measurements have been analysed in order to determine the seasonal fluctuation in rates of growth. The rate of increase in height appears to reach a maximum in the latter part of spring and a minimum in the middle of autumn. The rate of increase in weight appears to reach a maximum in the latter part of autumn and a minimum in the middle of spring. Tables and graphs are given showing, for each sex, the variation in the rates of growth throughout the calendar year. I wish to thank the County Medical Officer of Health, W. Allen Daley, M.D., F.R.C.P., for permission to publish this paper and for encouragement in its preparation; Mr L. Coward, F.I.A., and Mr E. Lewis Faning, Ph.D., for statistical criticism; and Mr J. H. Farrar for drawing the diagrams.The London County Council takes no responsibility for the views expressed in this paper which are personal only.