Surface configurations are vessels fabricated from tubing and plate, films deposited on the surface of vessels, and beads confined in vessels. The average association constant between thrombin and sites on commercial poly(methyl methacrylate) surface (Lucite) is near 4 X 10(8) liters/mole at 22 degrees C, pH 7.0, and ionic strength 0.15. Depending on Lucite composition, average adsorption U, in molecules/cm2 of apparent solution-surface interface, ranges from 0.7 to 8.8 X 10(11). Analysis based on the assumptions that solution dimensions are preserved, adsorption is random, and surface rearrangement is negligible indicates a paucity of surface sites. Plasma albumin competes with thrombin for surface sites. Attempts to detect, by thrombin adsorption, the presence of free sites at 4.5 X 10-9M albumin or the displacement of bound albumin indicate an albumin-site association contrast greater than 1.6 X 10(9). Cross-linked poly(methyl acrylate) bead surface has U less than 5 X 10(10). In contrast to acrylic resins are silicone gum, polypropylene, and polyisobutylene, for which U ranges from 15 to 20 X 10(11). Analysis as above indicates that sites are of frequent occurrence. Material composition suggests that thrombin can interact with nonpolar groups. Further characteristics of low-energy surfaces are that progressive surface denaturation is small and there is a large variance between nominally equivalent configurations.