The study of 25 samples of synovial membrane taken from 118 subjects with articular chondrocalcinosis makes it possible to identify three histological aspects : the complete forms showing a crystalline deposit of calcium pyrophosphate of variable volume and alterations of an inflammatory or degenerative type ; incomplete forms showing no calcium deposit, but in which one can observe two sorts of modifications : forms of chondroid metamorphism or inflammatory stigmatas causing an indeterminate chronic synovitis ; finally, forms of superficial fibrosis of the chorion are sometimes encountered. In all, the synovial membrane in articular chodrocalcinosis is often little different from an arthrosic or senile one. However, the presence of crystalline deposits rich in calcium and phosphorous and varying in size can, in the face of certain articular manifestations of uncertain cause, point to the existence of an articular chondrocalcinosis.