1. The rate of [14C]leucine incorporation into the protein of frog pepsinogenic cells was measured in both fasted and fed animals. The incorporation rate increases after feeding, becoming maximal after 2 h.
2. In the oesophagi of fasted frogs, only monoribosomes and dimers are present. The absence of polyribosomes is not due to autolysis in the homogenate. After feeding, heavy polyribosomal aggregates appear.
3. It is concluded that feeding stimulates protein synthesis in frog pepsinogenic cells.