A number of transient intermediates have been observed following conventional and nanosecond flash photolysis of plastoquinone-1 and plastoquinone-9. In alcohol solvents short-lived radical species decay to mixtures of cisoid- and transoid-o-quinone methides. The cisoid-methides ring close to plastochromenols whereas the transoid-methides undergo solvent addition giving rise to dihydrobenzofurans. Plastosemiquinones are also observed and these most probably decay by disproportionation to the o-quinone methides and plastohydroquinones. The biological implications of this work are briefly discussed.