Ten guinea pigs were exposed to 110 dB SPL white noise for 30 minuted and cochlear microphonics(CM) were measured at 500Hz, 1,000Hz and 2,000Hz with 100 dB SPL pure tone stimulation on round window membrane after 0, 15, 30, 45, 60 and 90 minutes by extracochlear electrode method. The CM response showed maximum decrease at 30 minutes after noise exposure. Five guinea pigs were exposed to 110dB SPL white noise for 30 minutes and CM were measured after 30 minutes(maximum decreased state of CM)at 500Hz, 1,000Hz and 2,000Hz with 90dB SPL pure tone stimulation. The spectrum of CM was analyzed by fast Fourier transformation and measured the amplitude ratio between fundamentals and second harmonics each frequency before and after noise exposure state. The results were as follows : 1) CM response gradually decreased until 30 minutes after white noise exposure and nearly completely recovered 90 minutes after exposure. 2) The second harmonics of sepctrum of CM was observed definitely at 90dB SPL pure tone stimulation, but it was not observed at 70dB SPL pure tone stimulation. 3) The amplitude ratio between fundamentals and second harmonics at 90dB SPL without noise exposure was 9.2 at 500Hz, 46.0 at 1,000Hz and 66.3 at 2,000Hz. 4) The amplitude ratio between fundamentals and second harmonics at 90dB SPL after noise exposure was 6.4 at 500Hz, 24.4 at 1,000Hz and 30.6 at 2,000Hz. 5) It seems to be that the second harmonics of spectrum of CM was observed by intense pure tone stimulation but its amplitude was increased and even third or fourth harmonics was observed in the CM recorded from guinea pig under temporary threshold shift state.