Twenty bacteremic strains of Staphylococcus epidermidis were characterized according to their hydrophobicity, their ability to produce slime, and their in vitro adhesion to polystyrene microtiter plates precoated or not with plasma proteins. Four strains of Staphylococcus aureus were also tested for adhesion. Slime production in S. epidermidis was not correlated with initial adhesion, whether measured qualitatively or by a quantitative method. Hydrophobicity (xylene:water partition) was well correlated with adhesion. Slime production, adhesion, and hydrophobicity were highly strain dependent among S. epidermidis organisms. For S. epidermidis, early adhesion was inhibited (10% to 98%) by albumin and fibronectin in all strains, by plasma (19 strains), and by fibrinogen (18 strains). Stimulation occurred for one strain with plasma and two strains with fibrinogen. In contrast, adhesion was inhibited by albumin and markedly stimulated (twofold to 14-fold) by plasma, fibrinogen, and fibronectin for the four strains of S. aureus. Early adhesion of S. epidermidis to polymer surface appears to depend mainly on hydrophobicity and is usually impaired by plasma proteins, albumin, fibrinogen and fibronectin; with a heterogeneous behavior among the different strains tested. Slime production would interpose secondarily, after the first attachment.