Histological and cytological changes in the submandibular glands of adult male mice arising during the growth of sarcoma-180 subcutaneous tumors were studied. The submandibular glands of the mice were examined by morphometric analysis at 1, 3, 6, 10, 20, 30 and 64 days after inoculation of the tumor cells. There was a slow increase in the relative cross-sectional area of the granular convoluted tubule (GCT) in the section of the submandibular gland of the animals as the tumors grew. The increased proportional area of the GCT was significantly different from that of the control's from day 30. However, the mean weight of the glands was not increased. The proportional area of the granular cluster in the cells of the GCT of tumor cells in inoculated animals decreased about 5% on the first day and then quickly increased by 16% on the third day in comparison with those of the controls, eventually reaching a maximum of 74% (control, 54%) by day 30. In addition, the average number of granules per GCT cell decreased in the first three days, then increased to normal levels from day 6, going above the normal level from day 20 of the tumor growth. These changes in the glands of tumor-bearing animals disappeared within 20 days after removal of the tumor. These results indicate that the growth of the sarcoma-180 subcutaneous tumor caused morphological changes in the GCT and GCT cells, suggesting an alternation in the requirements of the secretions contained in the granules, such as the epidermal growth factor, during the growth of the tumor.