Progenitor cell migration speed is a function of Fn concentration. Ten thousand FDCP-mix cells were inoculated into migration assays in 96-well plates as described in Materials and Methods and assayed at a 15° tilted position. Migrational movements of individual cells were analyzed by video microscopy for each experimental point, and the average speed was calculated. (A) Cultures at 10 U/mL IL-3, with varying Fn-coating concentrations as indicated, and (B) cultures precoated with 10 μg/cm2 Fn at varying concentrations of IL-3 as indicated. Results represent means ± SD of 6 to 8 determinations.