Observations on three obese persons on starvation diets are reported. Older findings about the rate of weight loss, reduction of the basal caloric requirement, the behavior of the respiratory quotient, the acid-base balance and the ketobody excretion have been confirmed. The effect of insulin on the non-diabetic ketosis has been demonstrated. The fat metabolism in starvation has been discussed and it has been found that Stadie’s theory of a utilization limit for fat and a threshold for ketosis is compatible with observations on starvation ketosis. The still remaining differences between starvation ketosis and diabetic ketosis are emphasized.