The ability of chondrosarcoma cell-derived preparations to stimulate an increase in the motility of bovine capillary endothelial (BCE) cells was quantitated using a phagokinetic track assay which measures the area of tracks produced by BCE cells after ingestion of gold particles. Chondrosarcoma preparations stimulated a 2-fold increase in the mean track area produced by BCE cells in an 18-h incubation period. The motility-stimulating activity of chondrosarcoma was purified about 120-fold. The most highly purified fractions had MW between 16,000 and 20,000 and stimulated a 2-fold increase in BCE cell motility at concentrations of 10 to 20 ng/ml.