In order to analyze the presence of alkaline and acid phosphatase activity in osteoarthrotic subchondral bone frozen sections from 24 femoral heads were prepared for semiquantitative analysis, using the enzyme-histochemical methods described by Burstone and by Barka and Anderson. Different areas of the subchondral bone, viz. weight-bearing, nonweight-bearing and osteophytes as well as central regions were analyzed. Furthermore, the cartilagenous changes were determined by histological-histochemical grading. There were wide variations within the same femoral head with significantly greater activity of both alkaline and acid phosphatase in weight-bearing than in nonweight-bearing areas and in subchondral bone than in central regions. Osteophytes excluded, the enzyme activities correlated directly with the severity of the cartilage lesions. These enzyme activities presumably reflect the degree of bone regeneration and bone resorption respectively.