Cold hardiness in Taxus baccata L. was investigated over the winter months in six widely-separated provenances of England. It was found that the degree of cold hardiness varied according to season, the maximum tolerance to cold normally being achieved in mid-winter (January). Hardiness declined rapidly in the early spring, when populations from all provenances proved to be vulnerable to tissue damage under severe frost conditions. Between-provenance variation was also examined, and proved to be largely random, displaying no marked clinal features. There is, however, no doubt that populations in the northeast of England are in greater potential danger of sustained tissue damage, especially during the spring months, than those elsewhere in the country; and this may explain the relative scarcity of stands of native yew