The effect of specific chemical functionalities on the adhesion of polymorphonuclear leukocytes (PMNs) under flow was investigated using a set of well-characterized, chemically functionalized surfaces prepared by selfassembly of alkanethiolate monolayers on gold surfaces. Terminal functionalities included CH 3 , CH 2 OH, COOH, and (OCH 2 CH 2 ) 3 OH groups. A new surface modification was used to incorporate a phosphorylcholine moiety on the hydroxyl-terminated monolayer. Surface modification was verified using contact-angle measurements, ellipsometry, and X-ray photoelectron spectroscopy. Adhesion on the surfaces was studied in the presence and absence of preadsorbed fibrinogen. Fibrinogen adsorption on selfassembled monolayers (SAMs) was quantified using radioisotope detection. PMN adhesion was found to be dependent on the monolayer's terminal functionality. Adhe-sion was higher on the hydrophobic CH 3 surface and the polar COOH monolayer. Leukocyte adhesion was least on the phosphorylcholine-rich surface, followed by the ethylene-oxide-containing monolayer. Cell adhesion also was low on the hydrophilic OH monolayer. Attachment was decreased with increasing shear rate, exhibiting a three-fold decrease between 20 and 100 s -1 . Fibrinogen adsorption was higher on the CH 3 monolayer but comparable for the other four SAMs. Preincubation of the surfaces with fibrinogen decreased adhesion on all SAMs examined.