In the present study we evaluated spontaneous and stimulated adherence of human monocytes to regenerated cellulose and polyacrylonitrile (AN69) membranes. Spontaneous adherence at 60 min was significantly higher for regenerated cellulose (28 +/- 2%, P < 0.001) than for AN69 (11 +/- 2) membranes. Stimuli such as bacterial lipopolysaccharide, TNF alpha, interleukin-1 and -6 as well as platelet-activating factor, but not IL-4, significantly enhanced adherence at 60 min to AN69 (28 to 30%). In contrast, adherence was not further inducible in the presence of regenerated cellulose. Both spontaneous and cytokine/bacterial lipopolysaccharide-stimulated adherence were significantly reduced by SDZ-63072, a specific platelet-activating factor receptor antagonist. This difference in sensitivity of monocyte adherence reflects probably the intrinsic ability of regenerated cellulose to provide maximal spontaneous monocyte adhesion. These data suggest that PAF may act as an adherence mediator. This is in line with the ability of regenerated cellulose to directly stimulate monocytes to synthesize platelet-activating factor and with the ability of cytokines and bacterial lipopolysaccharide to stimulate its synthesis. Although AN69 has a low adherence potential, bacterial lipopolysaccharide or cytokines may blunt the biocompatibility of this membrane.