The light response changes of oxygen evolutíon in the isolated spinách (Spinacia oleracea L.) thylakoids associated with the photoinhibition, influenced by the temperature and radical protection, were determined. Photoinhibition was performed at 20 ®C with or without an addition of antioxidant mixture consisting of glutathione, ascorbate, superoxide dismutase and catalase, oř, altematívely, at 0 oC without the antioxidants. Beside the effects on decline of atrazine binding sites and variable room temperature fluorescence, the three variants of photoinhibition differed with respect to their effects on the yield of oxygen evolutíon. Quantum yield of oxygen evolutíon (<{>02) flecline preceded Úie decrease of electron transport capacity at the beginning, while similar low values were found at the end of the treatment. In the presence of antioxidants the electron transport capacity remained high, whereas marked decline of (|»o^ occurred with the equally treated thylakoids. Comparable deviating behaviour of (t»Oj and the electron transport capacity was not found following photoinhibition at 0 oC; both were affected to the same degree, regardless if ferricyanide or the Qg- independent electron acceptor siUcomolybdate were ušed. With isolated thylakoids the quotient FyF,„, which is often ušed as a measure for photochemical efficiency of open photosystem 2 reaction centres in whole plant studies, did not decline to the same extent as (|)Oj under the dififerent photoinhibitoiy conditions applied. The main conclusion is that in thylakoid photoinhibition the independent mechanisms are associated with the changes of both the and electron transport capacity, and that the (j>02-related mechanism is inhibited at 0 oC.