The activity of alkaline phosphatase is increased significantly in the livers of rats after the intraperitoneal administration of nystatin. Studies with cycloheximide suggested that de novo protein synthesis was essential for the effect of nystatin on alkaline phosphatase activity. The induction of hepatic alkaline phosphatase by nystatin is not secondary to the release of glucocorticoids because the response of the enzyme to the administration of nystatin was not affected by bilateral adrenalectomy.