Dynamic processes in proteins and cell membranes, whose rates span the range 10' - 10'' s.', can be tracked by means of time-resolved two-step photoselection, which entails irradiating the specimen by a plane-polarized flash and observing the absorption or emission of light polarized parallel and perpendicular to the exciting flash. The technique is illustrated by discussing the ns and ,us dynamics of proteins (soluble and membranous) and platelet lipid bilayers involved in