The activity of chitinases in extracts obtained from the leaves of tomato, cultivars Julihirsutian (early repining) and Anatolie (late repining) was analyzed. The plants were grown in field conditions and each 10th day treated with the solutions of Reglalg, natural plant growth regulator. In extracts from the leaves of early repining cultivar, in control and experimental (plants treated with Reglalg) variants, the successive increasing of chitinases activity was observed. For the late repining cultivar a decline in enzyme activity was observed at the middle period of vegetation (by the end of June), followed by increasing of its activity in the late of July. Also, we note that in the extracts from the leaves of both cultivars, treated with Reglalg, the activity of chitinases was lower compared to those of control plants. Taking into consideration the beneficial effects of Reglalg on plant growth, we consider that the lower level of chitinases demonstrate the increasing of plants vigor, due to the beneficial effects of natural plant growth regulator.