Loss of CDC42GAP expression is associated with increased motility while directed migration is defective. Neutrophil migration was examined by time-lapse video microscopy in a gradient of 10 μM fMLP in a Zigmond chamber. (A) Representative images of cells during the course of migration; fMLP concentration increases from left to right. Videos S1-S3 have more representative images. WT cells orient and migrate toward the source of fMLP (arrows). CDC42GAP^–/– cells displayed abnormal membrane protrusion (arrows) and some cells migrated away from the gradient (arrowheads). (B) The percentage of cells displaying more than one membrane protrusion was enumerated. (C) The percentage of cells that migrated away from high fMLP concentration is indicated in the histogram. (D) The average translocation rate was measured using Openlab. The result from freshly isolated neutrophils is shown. Similar results were obtained from neutrophils generated in in vitro culture. All histograms represent the mean ± SD; n = 23 to 25 cells from 2 to 3 independent videos.