The F-actin based, microfilamentous cytoskeleton (MFC) provides mobility for phagocytic immune cells including the polymorphonuclear leukocyte (PMN) and macrophage (MO). In PMNs in suspension, the MFC is organized into two distinct F-actin pools (Triton Insoluble F-actin-(TIF) which forms the submembranous, 3D actin meshwork and Triton Soluble F-actin (TSF) which exists as short oligomers) in equilibrium with G-actin. The structure of F-actin pools in adherent cells is unknown despite the fact that phagocytes are adherent in tissues in vivo. In order to determine the structure of F-actin pools in adherent phagocytes, human PMNs were isolated and allowed to adhere to plastic for 1 hour at 37°C. Adherent cells were collected, actin pools separated and quantified by SDS-PAGE and compared to non-adherent PMNs in suspension. Likewise, the non-adherent human myeloid cell line U937 was induced to MO morphology and adherence by exposure to TPA (10-6 M × 3 days) and similarly evaluated. Adherence of PMNs to plastic resulted in 75±15% adherence (n=3). TPA differentiation of U937 cells resulted in 81± 15% adherence (n=10). In both cells, adherence resulted in a statistically significant increase in TIF and decreases in TSF and G-actin. Basal, non-adherent PMNs in suspension contain TIF 40± 0%, TSF 20± 4%, and G-actin 40 ±4%, n=3, while adherent PMNs contain TIF 61± 3%, TSF 5±5%, G-actin 34±1%. Basal U937 contain TIF 41± 9%, TSF 17± 6%, and G-actin 42±13%, n=7. Adherent MO-like U937 contain TIF 53±4%, TSF 9± 5% and G-actin 38± 4%. The results show that phagocyte adherence leads to a characteristic reorganization of actin pool structure, remarkably quantitatively similar to reorganization by chemotactic factor activation in suspension. The results suggest that despite differences in mechanisms of actin reorganization by chemotactic factor and adherence, the final common effect on cytoskeletal organization is similar.