WE have tried to establish whether or not lysozyme added in appropriate concentrations to human tumour cell cultures can produce some morphological changes in such cells. The following human tumour cells were utilized : strain Af (H.Ep 2) of epithelial nature and strain A (H.S. 1) of mesenchymal origin. These strains were kindly supplied by Dr. A. Fjelde, State Serum Institute, Copenhagen.