Light-driven chlorophyll a fluorescence quenching and dark reversibility of this process was measured in LHC II — the major light-harvesting pigment-protein complex of Photosystem II. Two preparations of LHC II, complex isolated from dark-adapted (LHC II-D) and light-pretreated (LHC II-L) rye leaves, differed significantly in the level of the xanthophyll pigment violaxanthin, being enriched in LHC II-D. LHC II-L contained only trace amounts of zeaxanthin but additionally antheraxanthin. LHC II-D suspended in buffer showed similar fluorescence quenching kinetics. Chlorophyll fluorescence quenching in LHC II-L was almost fully reversible after 2 h of dark-adaptation whereas only 37% of the initial fluorescence level was recovered under identical conditions. Transfer of LHC II as protein-lipid complex (PLC) in a reverse micellar solution composed of isooctane, phospholipids and limited amount of water, considerably decreased xanthophyll pigment concentrations. Under these conditions, light-driven fluorescence chlorophyll a quenching was the same for LHC II-L and LHC II-D and fluorescence level in both preparations was fully reversible within the dark period. Kinetics of light-induced fluorescence quenching and reversibility of LHC II-L reconstituted in asolectin liposomes was faster than in buffer. However, reversibility of LHC II-L in liposomes was markedly slowed down by addition of exogenous xanthophyll pigments in the following sequence: violaxanthin > zeaxanthin > nonpigmented liposomes. Remarkable light-dependent changes in chlorophyll a fluorescence excitation spectra of LHC II-L in liposomes were observed. These changes are ascribed to energetic uncoupling caused by physical detachment of violaxanthin from the antenna complex — this process being discussed in terms of violaxanthin availability to de-epoxidation in thylakoid membrane. The possible involvement of the xanthophyll cycle pigments violaxanthin and zeaxanthin in the regulation of light-driven excitation quenching in LHC II is also discussed.