We present a method for the quantification of the fast plasma membrane movements that are involved in ruffling, blebbing, fast shape change, and fast translocation. The method is based on the Kontron Vidas image analysis computer program. Video images from cells viewed through an inverted microscope were transmitted to the computer. The procedure was as follows: 4 consecutive video images were averaged (imagel); 28 s later a second set of 4 video images was averaged (image 2); image 2 was subtracted from image 1 and the grey level of each pixel of the resulting image was increased with 128 grey level units, resulting in the subtraction image, showing a uniform grey background speckled with brighter and darker spots corresponding to areas of movement. These spots were discriminated and turned into white objects against a black background. Interactive editing was used to delete artefacts that resulted from floating debris. The total area of the discriminated objects was measured, and the parameter motile area in pm2 per cell was calculated. We have applied our method to the study of motility induced in epithelial cell lines by the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate and by epidermal growth factor.Key terms: Cell motility, cell membrane, cell-surface, ruffling, blebbing, cellshape, translocation, image analysis, TPA, EGF Direct analysis of cell motility in vivo is problematic because of the lack of transparency of three-dimensional living tissues. There is evidence indicating that the study of cell motility on a flat surface in vitro is relevant for the situation in vivo because cells have an inherent motility program (11,12,21). Various aspects of cell motility (see Methods for terminology used in this paper) can be assessed in vitro. Several methods have been described to quantify translocation (7,15,23), directional migration including chemokinesis and chemotaxis (13,251, as well as shape change (17,24). Quantification of fast plasma membrane movements involved in ruffling, blebbing, formation or movement of cytopodia, and fast shape change or fast translocation has received less attention. Partin et al. (17) have described an elaborate Fourier analysis for quantification of the various aspects of cell motility, including ruffling. Recently Tatsuka et al. (22) described a method for quantification of "momentary alterations of cell shape" reflecting ruff ling, pseudopodal activity, and fast cell translocation, using automatic image analysis on Allen video-enhanced contrast-differential interference contrast images. Here, we report on a simple and rapid method for quantification of fast plasma membrane movements. It is entirely based on the Vidas automatic grey level image analysis program that is commercially available from Kontron (Eching, West Germany). We have tested our method on cell cultures differing in their type or intensity of motility as estimated from time-lapse video films. As an application of our method we analysed the effect of the tumor promoter 12-0-tetradecanoyl-phorbol-13-acet...