The concentration dependence of PCARS intensity has been measured for the 992 cm(-1) band of benzene in five different solvents and compared with that of Rayleigh scattering intensity. The temperature dependence of PCARS and Rayleigh scattering has also been studied for neat benzene. The concentration dependence of PCARS and Rayleigh scattering shows a similar correlation to the refractive index difference between benzene and the solvents. It is shown that PCARS cannot be considered as the Rayleigh scattering of the (phase mismatched) CARS radiation, by comparing the concentration and temperature dependence of their intensities. The fluctuation of the third-order nonlinear susceptibility itself plays an important role in PCARS. This means that PCARS may bear unique information on the microscopic properties of liquids that Rayleigh scattering can not provide.