Abstract A single dose of penitrem A (2·5 mg per kg, i.p.) in propylene glycol caused a 53% decrease in mouse liver DNA. Total liver lipid was increased 178% at 24 hr. A disappearance of free fatty acids concomitant with an increase in liver triacylglycerols also was detected. Total liver glycogen decreased 68% by 6 hr after similar treatment but returned to pretreatment levels by 48 hr. Liver sections from animals given 2·5 mg per kg penitrem A showed slight degranulation of centrolobular hepatocytes. In contrast, liver glycogen in fasted animals was increased 92%, 72 hr after dosing with 2·5 mg per kg penitrem A. Four consecutive daily i.p. administrations, totaling 4·0 mg per kg of penitrem A, resulted in reduced food consumption and a suppression of animal growth. DNA levels were significantly lower, whereas glycogen was significantly elevated in the liver of these animals. Cholesteryl esters in livers obtained from this group of treated animals were the only lipids which were significantly elevated.