1. Cytoplasmic inclusions were found in the epithelial cells of the small intestine in a major proportion of suckling mice suffering from the spontaneous or experimentally produced diarrheal disease now prevalent in this laboratory.
2. They were not found in healthy stock mice of corresponding age.
3. Feeding of intestinal extract from healthy mice did not produce diarrhea or inclusions.
4. Feeding of boiled extract from diarrheal mice did not lead to the formation of cytoplasmic inclusions, when precautions were taken to prevent accidental infection.
5. The inclusions were regularly present only in the first few days of the disease. The inclusion-bearing cells desquamated. There was no inflammatory reaction.
6. Attention is called to the frequent presence of large numbers of Gram-positive coccoid bodies in the intestinal contents of suckling mice with diarrhea.