The results of leaf chlorophyll fluorescence measurements of crop oat cv. Akt and wild oat subjected to Dicuran 80 WP (a.s. chlortoluron) herbicide with two adjuvants (Adpros 85 SL, Atpolan 80 EC) are presented. Chlortoluron, as a phenyl-urea herbicide, is an inhibitor of photosynthetic electron transport in photosystem II, which can be measured by means of the special pulse PAM-210 fluorometer as ETR (electron transport rate) parameter. Dicuran 80 WP, applied alone in concentration of 0.5 mmol dm-3, caused a decrease in ETR value in the wild oat leaves, whereas it did not affect the crop oat. The adjuvants Adpros 85 SL and Atpolan 80 EC added to Dicuran amplified the action of this herbicide.