Photochemical efficiency of photosystem 2 (PS2), assessed from in situ chlorophyll (Chl) fluorescence measurements, was seasonally monitored in five evergreen sclerophyll and five malacophyllous drought semi-deciduous species, co-occurring in the same Mediterranean field site. In evergreen sclerophylls, a considerable drop in the variable (Fv) to maximum (Fm) Chl fluorescence ratio coincided with the lowest winter temperatures, indicating low PS2 efficiency during this period. Summer drought caused a comparatively slight decrease in Fv/Fm and only in three of the five evergreen sclerophyll species tested. In drought semi-deciduous shrubs, the winter drop in Fv/Fm was much less conspicuous. During the summer, and in spite of the severe and prolonged desiccation of their malacophyllous leaves, Fv/Fm was maintained high and only in one species the PS2 efficiency was transiently suppressed, when the leaf relative water content became lower than 30 %. Thus evergreen sclerophylls are more prone to photoinhibition by low winter temperatures, while the sensitivity of drought semi-deciduals depends on the extent and duration of summer drought. and S. Karavatas, Y. Manetas.