Angiogenesis is a multistep process intimately involved in embryonic development and subsequent cardiovascular homeostasis and pathology. A major event in the process of angiogenesis is endothelial cell migration. Common in vitro assays (filter, under-agarose, phagokinetic track) used for the evaluation of migration are interpreted by measurements such as leading front distance, total cells migrated, and total area of migration. However, these quantities depend very heavily upon the physical aspects of the assay such as geometry, chemoattractant concentration and diffusivity, and observation time. Thus, while these common cell motility measurements are convenient, they do not represent solely the intrinsic cell response to an attractant. Alternatively, cell motility responses can be described by parameters which do not depend on the physical aspects of the assay system. Such parameters, termed phenomenologic parameters, have been defined for cell migration in a mathematical model derived by others. This model defines two parameters, the random motility coefficient, mu, and the chemotaxis coefficient, chi, which describe the migration responses to uniform concentrations and to gradients of stimulant, respectively. We have used this approach to evaluate the random motility response of human microvessel endothelial cells isolated from omental fat. Human microvessel endothelial cell random motility was measured in uniform concentrations of heparin (10(-3) to 10(3) micrograms/ml) using an under-agarose assay with linear geometry. The value of mu was found to remain constant at 8.2 x 10(-9) cm2/second for all concentrations tested and without heparin. These data indicate that heparin at these concentrations does not significantly stimulate random migration of human microvessel endothelial cell. These results suggest that the potentiating effect of heparin on angiogenesis may not be mediated through a direct affect on endothelial cell migration. Because the random motility coefficient and chemotaxis coefficient are representative of intrinsic cell motility behavior, their use should provide more specific information on endothelial cell migration than other commonly used measurements.