Phenylboric acid in total amounts of 25 resp. 50 μ g was applicated to the apex of young plants of Coleus blumei, Impatiens sultani, Bryophyllum calycinum, Lycopersicon esculentum and cuttings of a hybrid of Populus balsamifera in the course of 5 weeks. In most cases the application results in rising the contents of storage carbohydrates, especially in the overground parts of plants. The effect is marked only in those species, in which a significant inhibition of longitudinal growth occurred. Usually, the contents of dominating storage carbohydrates increase most. There are no seasonal differences in the effects of phenylboric acid on the behaviour of carbohydrates. The increase of the amounts of storage carbohydrates is suggested to be a consequence of the inhibition of growth. There is no certain indication to a direct influence of phenylboric acid on carbohydrate metabolism.