Apparent molar volume and enthalpy changes for mixing NaCl (aq.) with lysozyme (aq.) are experimentally determined. The enthalpy change generally becomes more exothermic as the concentration of NaCl increases but exhibits a maximum exothermic effect at 0.68 m NaCl. The apparent molar volume exhibits a minimum at 0.3 m NaCl and a maximum at 0.68 m NaCl with a difference of 3.9 x 10(2) cm(3) mol(-1). The apparent molar volume increment for the process driven by Li2SO4, MgCl2 and (NH4)(2)SO4 is similar, 3.4 x 10(2) cm(3) mol(-1). (c) 2005 Elsevier B.V. All rights reserved.