Seasonal variations of recovery of liver monoamine oxidase activity were studied in different subcellular fractions after administration of a large dose of pargyline in vivo. It was shown that the recovery of cytosolic MAO differs greatly from the membrane bound forms in the rate of reconstitution of its activity upon irreversible inhibition in vivo. Alcoholization leads to a decrease of the rate of recovery of only the membrane-bound but not a cytosolic MAO B forms in rat liver.