Seedlings of spring barley, meadow fescue, and winter rape were fumigated with 180 μg kg-1 of ozone for 12 d, and effect of O3 on photosynthesis and cell membrane permeability of fumigated plants was determined. Electrolyte leakage and chlorophyll fluorescence were measured after 6, 9, and 12 d of fumigation, while net photosynthetic rate (PN) and stomatal conductance (gs) were measured 9 d after the start of ozone exposure. O3 treatment did not change membrane permeability in fescue and barley leaves, while in rape a significant decrease in ion leakage was noted within the whole experiment. O3 did not change the photochemical efficiency of photosystem 2 (PS2), i.e., Fv/Fm, and the initial fluorescence (F0). The values of half-rise time (t1/2) from F0 to maximal fluorescence (Fm) decreased in fescue and barley after 6 and 9 d of fumigation. PN decreased significantly in ozonated plants, in the three species. The greatest decrease in PN was observed in ozonated barley plants (17 % of the control). The ozone-induced decrease in PN was due to the closure of stomata. Rape was more resistant to ozone than fescue or barley. Apparently, the rape plants show a large adaptation to ozone and prevent loss of membrane integrity leading to ion leakage. and A. Plażek, M. Rapacz. A. Skoczowski.