Cambial and phellogen activities in Pistacia lentiscus were followed by the radiological method. Under natural conditions xylem was produced in most cases during two separate seasons of the year, i.e. spring and autumn. The phloem was produced during two different periods that were shorter than those of the xylem production. The phellogen was active once a year in some branches, during the end of April and May. The cambium of irrigated plants was continuously active throughout the spring, summer and autumn. The cessation of activity of the lateral meristems during the winter and summer seems to represent rest periods. The pattern of activity of the lateral meristems in Pistacia lentiscus suggests that this species is weil adapted to the Mediterranean climatic rhythm.