The binding reactions of the fluoroquinolone with bovine serum albumin (BSA) were investigated by microcalorimetry. The thermodynamic parameters were measured with the help of spectroscopy in a Tris-HCI buffer solution (pH 7.0, made isotonic with sodium chloride) at T = 298 K. Microcalorimetric measurements show that the molar change of enthalpy Delta H-r(m) is insignificant for the reaction, which may suggest that the interaction is governed mainly by entropy, and the iriteraction between the protein and the drugs is stronger. The results also reveal an entropy-enthalpy compensation relationship of the interaction. (c) 2006 Elsevier Ltd. All rights reserved.