Summary The effects of curing temperature and age on the strength of concrete can be expressed in terms of a single parameter given by the product of age and temperature, as has been suggested by Nurse.(1)*· and Saul.(2) In this parameter, the temperature is reckoned from — l0°C, which seems to be a reasonable value of the lowest temperature at which any appreciable increase in strength can take place. In the present paper, the correctness of this assumption is verified by means of check calculations made on previously known test series and on some new Swedish tests. It is to be noted, however, that special precautions must be taken to protect the concrete from freezing during the initial period after placing, and that the humidity of the ambient air must be taken into account. Moreover, the deterioration of concrete subjected to repeated freezing and thawing must be studied as a separate problem.