Tritium-labeled vitamin A acetate was administered intravenously to calves fed adequate vitamin A and carotene. Declining specific activity of vitamin A in biopsy samples of liver and detection of radioactivity in the blood throughout the 93-day experiment indicated continuous turnover of liver vitamin A. Radioactivity was also detected in urine and feces. Average half-time of liver vitamin A was 48 days with a standard error of 4.