Alkaline phosphatase activity increased 10,000-fold over basal levels in reindeer antler during the period of massive growth. The activity was highest in the zone of differentiating chondrogenic cells in the growing tip. The activity in the shaft was lower. PPiase activity was also highest in the antler tip, but compared to alkaline phosphatase, was more tightly membrane-bound. Ca2+, Mg2+-ATPase activity was not so markedly elevated in the tip as were the other activities. During the growth cycle, the highest activities of acid phosphatase and amino peptidases occurred later than the peak of alkaline phosphatase activity, and were found mainly in the dermis of the shaft.