We previously demonstrated that the f-actin cytoskeleton modulates oxygen radical production associated with polymorphonuclear leukocyte (PMN) oxidative burst activity. Given the close association of the actin and microtubule cytoskeletons with the plasma membrane and the transmembrane location of the PMN NADPH oxidase, it is likely cytoskeletal change may affect PMN membrane responses, such as cellular anisotropy. Changes in PMN membrane fluidity were therefore examined after PMN activation by the chemoattractant N-formyl-1-methionyl-1-leucyl-1-phenylalanine (fMLP) in the presence or absence of phalloidin or cytochalasin B (CB), agents that stabilize and disrupt f-actin, or taxol and vincristine, which stabilize and disrupt microtubules, respectively. Phalloidin and taxol treatment of PMN significantly decreased whereas CB and vincristine significantly increased membrane fluidity. Activation of PMN by fMLP (10(-6) M) resulted in a significant increase in membrane fluidity that was attenuated by PMN pretreatment with phalloidin or taxol. CB and vincristine pretreatment of PMN did not alter the fMLP response. These data suggest that stabilization of the f-actin or microtubule cytoskeleton may prevent increases in cellular membrane fluidity associated with PMN activation.