The effects of drought oř salinity (NaCl) stress in combination wifh high irradiance (HI) were studied under the laboratory conditions, using young plants of a drought- resistant cultivar of Sorghum bicolor in order to understand leaf observed effects at the chloroplast level. Water potential and net photosynthetic rate (P^j) in leaves were analyzed in parallel with photosynthetic electron transport, electron spin resonance and chlorophyll-protein (CP) composition in chloroplasts isolated from these stressed leaves. The H1 slightly increased and electron transport activities of the irrigated plants, whereas drougbt and salinity stresses (leaf water potential lower than -1 MPa) decreased these activities. Under the combined effects of drought or salinity stress (200 mM NaCl) with HI the leaf Pjj was severely inhibited, as were photosystem (PS) 2 chloroplast electron transport activities (but not PS 1 activity). NaCl concentrations lower than 100 mM stimulated the electron transport activities in non-photoinhibited plants. A degradation of the PS 2 CFs and a decrease of ESR signál n were seen in the drought and salinity stressed plants afler HI.