1. Using fibroblasts from chick embryo hearts and puppy cerebellar cortices cultivated by a roller-tube method, a study was made on the changes of lysosomes under anaerobic conditions attained by a modification of SCHOETTENSACK's method.
2. It was found that lysosomes were markedly decreased in number in fibroblasts cultured anaerobically and this decrease in number of lysosomes was accompanied by a concomitant appearance or increase in number of degenerative phospholipid granules devoid of acid phosphatase activity.