Hb adsorption to foreign surfaces was not previously considered in studies of blood-material interactions, despite the fact that Hb is the most abundant protein present in blood. A Hb-like protein was detected on a number of surfaces exposed to [bovine] blood plasma, serum and red cell suspensions. Hb adsorption to polyethylene from plasma approximately equalled the amount of adsorption of albumin and fibrinogen. The high relative affinity of Hb for polyethylene was further confirmed by adsorption isotherm and direct competition experiments. The data from all 4 experimental methods support the following ranking of plasma protein affinity for polyethylene: Hb .mchgt. fibrinogen > albumin .simeq. .gamma.-globulin.