A proteolytic enzyme, alpha-chymotrypsin, and a lipolytic enzyme, cutinase, were adsorbed from aqueous solution onto a hydrophobic Teflon surface and a hydrophilic silica surface. We investigated the influence of adsorption on the structure, the structure thermal stability and the activity of these enzymes. Probing the protein structure by circular dichroism spectroscopy indicates that Teflon promotes the formation of helical structure in alpha-chymotrypsin, but the reverse effect is found with cutinase. The perturbed protein structures on Teflon are remarkably stable, showing no heat-induced structural transitions up to 100 degrees C, as monitored by differential scanning calorimetry. Contact with the hydrophilic silica surface leads to a loss in the helix content of both proteins. Differential scanning calorimetry points to a heterogeneous population of adsorbed protein molecules with respect to their conformational states. The fraction of the native-like conformation in the adsorbed layer increases with increasing coverage of the silica surface by the proteins. The specific enzymatic activity in the adsorbed state qualitatively correlates with the fraction of proteins in the nativelike conformation.