OBJECTIVE To investigate the effect of propofol and its solvent Intralipid on the adhesion of activated platelets to leukocytes in vitro. METHODS Prospective study in an experimental laboratory. METHODS Sixteen healthy volunteers. METHODS Whole blood was incubated for 60 min with propofol (4, 40 micro g/ml), an equal volume of Intralipid 10% or phosphate-buffered saline (PBS). After stimulation with adenosine-5-diphosphate (ADP) platelet-leukocyte adhesion and platelet surface expression of P-selectin, GPIb and fibrinogen-binding to platelets were evaluated by flow cytometry. RESULTS The 4 micro g/ml concentration of propofol did not alter binding of platelets to leukocytes, expression of P-selectin, GPIb and fibrinogen binding to platelets. The 40 micro g/ml concentration of propofol reduced spontaneous and ADP-induced formation of platelet-neutrophil conjugates compared with PBS and the equal volume of Intralipid. In addition, binding of ADP-activated platelets to monocytes were also inhibited by 40 micro g/ml propofol. Following incubation with propofol, platelets showed reduced binding of fibrinogen in the unstimulated and ADP-stimulated blood samples as well as a lower percentage of platelets with bound fibrinogen. Effects dependent on the solvent Intralipid were enhanced adhesion of platelets to monocytes in comparison with propofol (40 micro g/ml) and PBS. CONCLUSIONS In clinically used concentrations, propofol does not alter the adhesion of platelets to leukocytes in vitro. At ten-fold anesthetic concentration propofol reduced the formation of platelet-neutrophil and platelet-monocyte conjugates. We suggest that this effect is due to an inhibition of fibrinogen-binding to platelets by propofol. These effects were all independent of the propofol carrier Intralipid.