Behavioral responses of D. chromatophora cercariae to light were studied in laboratory experiments. Cercariae demonstrated positive phototaxis that was especially pronoun- ced during the first hour of cercarial free life in the environment. After 6 h, the photoreac- tion is weakened but it retains the character of positive phototaxis. The photo-orientation helps cercariae to localize themselves in the areas of the water body ("host-space") where contact with the second intermediate host (fish fry) is most likely. It is assumed that the increase of the locomotory activity in D. chromratophora cercariae under sudden shading or lighting should be considered as a case of manifestation of the "fifixed behaviuor" trigged