A method for monitoring respiratory chain (RC) activity in single live cells is described. It is based on the registration of the photothermal (PT) response after a laser pulse of a live single cell. The dependence of the PT-response amplitude and shape upon redox state of RC components was studied with a PT microscope for two in vitro models: (1) solutions of the RC component cytochrome c and (2) mice hepatocytes. The parameters of the PT responses differed for oxidized and reduced forms of cytochrome c solutions and for inhibited RC and intact RC. The latter difference may be caused by alteration of the quantum yields of thermal (nonradiative) relaxation for light-absorbing molecules, i.e. RC components, as they undergo reduction during RC inhibition.