Summary:Within 24 h time, Torak EC 24 in 10 mg/l and 30 mg/l concentrations causes the worst damage immediately after treatment. In the treated hydras, a considerable state of contraction, a damage of tentacles and the hypostome as well as a damage of intracellular membranes and cellular organelles was observed. Besides, during the experiment, the treated hydras in both concentrations used were budding more intensely than the control.