1. Cultivation of freshly explanted chick embryonic heart tissues in Hanks's salt solution for 3 to 4 days has been shown to create a general state of nutritional deficiency in the cultures. Provided the depletion is not prolonged beyond 4 days, the cultures subsequently revive and survive to a normal period in synthetic medium M 150.
2. Paper chromatographic studies on the culture medium have shown that the amino acid metabolism of the depleted cultures is restored to a normal pattern within a few days in medium M 150.
3. By the use of the nutritional deficiency technique, a coenzyme A requirement for this type of culture has been established.
4. The application of these findings to tissue cell nutrition and the possible hazards of using serum, or other uncharacterized additions, either to establish cultures, or as part of the experimental medium, are discussed.