Cucumber (Cucumis sativus L. cv. Dar) leaves exposed to UV-B irradiation at a biologically effective dose of 9.5 kJ m-2d-1 showed decreased chlorophyll fluorescence parameter values versus the control; in peppermint (Mentha piperita L. cv. Asia) leaves those values were almost unchanged after treatment. Fv/Fo and Rfd were reduced more than other values, indicating inhibition of the oxygen-evolving complex and cooperation between the light and dark photosynthesis reactions as the primary targets of UV-B. The photosynthetic electron transport rate showed less change directly after irradiation, but after 24 h of recovery it was reduced to 50% of the control. Generally, photosystem II of peppermint leaves appeared more tolerant to the applied UV-B radiation than in cucumber leaves.