In this paper, the adsorption of bovine serum albumin on polypropylene glycol-sepharose gel under both the linear and nonlinear hydrophobic interaction chromatography (HIC) conditions is described. Characterization of behavior was pursued through a combination of flow microcalorimetry, linear chromatography, and isotherm measurements. It is shown that these measurements support the strong influences of water release and protein conformation in the HIC process. It has also been shown that the Van't Hoff analysis does not provide reasonable estimates of the heat of adsorption under nonlinear conditions.