Lysophosphatidylcholine and lysophosphatidylethanolamine levels were determined during Sr2+-induced oscillating ion fluxes in mitochondria prelabelled in vivo with 32Pi. Periodic fluctuations of both lyso compounds were established with an increase at the stage of simultaneously monitored K+ influx and a decrease at K+ efflux. The periodic activations and inactivations of phospholipase were found to be associated with periodic changes in the incorporation rates of labelled polyunsaturated fatty acids with an apparent phase difference of 180 degrees. Periodic deacylation-acylation cycles of phospholipids accompanying the periodic cycles of reversible ion accumulation and release are suggested to be involved in the trigger mechanism generating the permeability changes during oscillatory ion transport.