The technique of microelectrode has been used to record receptor potentials of outer hair cell (OHC) of seven guinea pigs' cochlea basing on the programmable signal processing system. The nonlinearies of input-output function of the receptor potential recorded from OHC are compared before and after with noise exposure. Results indicated that the input-output functions of the receptor potential of OHC reveal linear behavior increased in linearity in low level and turned to be nonlinear when the sound level increased to 50 dB SPL, and significant saturation was seen in 80 dB SPL. After the white noise exposure (100 dB SPL , 10-20 minutes), the phenomenon of nonlinearity disappeared with the amplitude of receptor potential decreased, which suggested that nonlinearity was easy affected by noise exposure. OHC response recruitment has shown after noise exposure. These results together with preceding clinical observation of loudness recruitment, suggest that loudness recruitment occurs at least in part at the hair cell level.