The effect of alpha-monochlornaphthalene (MCN) on the level of vitamin A in blood sera and a storage of this vitamin in the liver of chickens was assayed. The experimental birds were given directly into the gizzard the MCN at doses from 5 to 200 mg/kg bw for 2 weeks. The level of vitamin A was determined by the method of Carr-Price four times: before the experiment, after the application of the two last doses of the MCN and after 2 and 4 weeks after the application of the last dose of the preparate. It was found that the MCN applied in high doses (100—200 mg/kg bw/day) decreased significantly the level of vitamin A in blood and in the liver. The decrease of the vitamin A in blood persisted for longer time, and this level did not return to the initial value by end of the experiment.