1. Sterile, cell-free saline extracts of the necrotic portion of methylcholanthrene-induced hamster sarcoma injected into non-tumor bearing hamsters produced a statistically significant decrease in hemoglobin, hematocrit and red blood cell levels.
2. These changes in hemoglobin, hematocrit and red blood cells are comparable to those observed during sarcoma growth.
3. Sterile, cell-free, extracts of viable sarcoma injected into hamsters failed to produce alterations in the hemoglobin, hematocrit or red blood cell values.
4. The necrosis produced during sarcoma growth in the hamster cheek pouch is concluded to be responsible for alterations in the red blood cell counts, hemoglobin and hematocrit values.