The distribution of cuboid crystals in articular cartilage was examined by image analysis of electron micrographs. The specimens were considered to be functionally normal articular cartilage from femoral heads resected either because of femoral neck fracture or tumour in the distal femur. The study was restricted to the superficial region between 0 and 50 microns depth. Crystals were present in all specimens regardless of the age of the patient. The crystal profile area density was significantly greater in superior region samples than inferior region samples and this difference was less in older specimens. A band of microcrystals 10-20 microns below the articular surface was observed in superior samples. A significant correlation between mean individual crystal profile area and age was observed. It is noted that crystals are present in regions of cartilage subject to high mechanical stress.