SUMMARYExcretion of C14‐labeled organic material byDunaliella tertiolectawas observed under a variety of conditions. In healthy cultures, percent excretion tints related to cell density bill independent of light and preconditioning of the medium. Exaction was lower in nutrient‐limited culture than in an enriched medium, and in both cases was minimal during logarithmic growth. Increases in dissolved carbohydrate during stationary phase represented an accumulation of high molecular weight compounds.The general composition of labeled excretory products was similar in both actively growing and stationary cultures. The data suggest that excretion may involve different processes at high and low cell densit