Dynamic Morphology is the attempt to correlate surface architec ture and shape of fixed cells, as visualized by scanning electron microscopy (SEM), with the behavior of living cells, recorded by microcinematography (MCM). If SEM and MCM are used concurrently for the analysis of cell populations, a dynamic inter pretation of SEM photographs is only valid if the experimental conditions are identical for the two techniques. This is achieved by allowing the cells to settle on a glass surface where they remain long enough to perform their various activities under conditions identical for both techniques (for technical details see Methodology). The analysis of a population necessitates the study of a large number of cells. This prerequisite is met by operating the scanning electron micro scope at low levels of magnification, and by using culture chambers for cinematography. It can be argued that the examina tion of attached cells excludes a complete SEM survey of a population, as cells not adhering from the outset or becoming detached during the different preparatory steps are lost. For this, cinematography proved to be a reliable control: All cell types recognized in time-lapse films were also seen in scanning electron (SE) micrographs. Another, and more general, objection to a dynamic interpretation concerns the artificiality of cellular behavior on glass. This is true, but does not invalidate compara tive studies making use of this substrate.