Flash-induced voltage changes (electrogenic events) in photosystem I particles from spinach, oriented in a phospholipid layer, have been studied at room temperature on a time scale ranging from 1 mu s to several seconds. A phospholipid layer containing photosystem I particles was adsorbed to a Teflon film separating two aqueous compartments. Voltage changes were measured across electrodes immersed in the compartments. In the absence of added electron donors and accepters, a multiphasic voltage increase, associated with charge separation, was followed by a decrease, associated with charge recombination. Several kinetic phases were resolved: a rapid (<1 mu s) increase, ascribed to electron transfer from the primary electron donor P700 to the iron-sulfur electron acceptor F-B, was followed by a slower, biphasic increase with time constants of 30 and 200 mu s. The 30-mu s phase is assigned to electron transfer from F-B to the iron-sulfur center F-A. The voltage decrease had a time constant of 90 ms, ascribed to charge recombination from F-A to P700. Upon chemical prereduction of F-A and F-B the 30- and 200-mu s phases disappeared and the decay time constant was accelerated to 330 mu s, assigned to charge recombination from the phylloquinone electron acceptor (A(1)) or the iron-sulfur center F-X to P700.