Chlorophyll (Chl) fluorescence decay measurements were performed on higher plant leaves to investigate the photoprotective mechanisms under in vivo conditions. Measurements on leaves with different amounts of zeaxanthin pointed out that zeaxanthin is necessary for most of the observed nonphotochemical energy quenching, that has to be activated by a transthylakoid ΔpH. An additional sustained energy quenching component was clearly resolved in leaves with high amounts of zeaxanthin. The changes of the Chl fluorescence decay parameters did not correlate with a photoprotective energy dissipation in the reaction centre of photosystem 2 (P680), nor with a ΔpH-mediated, zeaxanthin-independent aggregation of the antenna complexes; no indications for a state 1/state 2 transition of the main light-harvesting complex LHC2 were found.