Calcific deposits in the menisci of the knees of 215 cadavera were characterized roentgenographically and crystallographically as part of a study of the pathological basis of calcium pyrophosphate dihydrate crystal deposition disease. Deposits of a primary type were found in multiple cartilages in 5.6 per cent of cadavera: in 3.3 per cent the deposits were composed of calcium pyrophosphate dihydrate (Ca₂P₂ O₇-2H₂O) and in 2.3 per cent, of dicalcium phosphate dihydrate (CaHPO₄-2H₂O). Solitary deposits of the secondary type, composed of hydroxyapatite, were found in 1.4 per cent of cadavera.

The implications of these findings are discussed as they affect (1) the possible prevalence of calcium pyrophosphate dihydrate crystal deposition disease, (2) the traditional classification of pathological calcification of cartilage, and (3) the roentgenographic interpretation of meniscal calcification. The crystalline compounds of the three-component system CaO—P₂O₅—H₂O that persist in soil as fertilizer are the same as the compounds identified in the meniseal deposits. Appropriate data from the soil chemistry literature are cited briefly as they provide background for speculation and future work on the mechanisms and significance of pathological calcifications in cartilage.