This study was undertaken to clarify individual differences in psycho-physiological responses observed in subjects listening to music. Forty-five healthy females listened to the third movement of Mozart's "Eine Kleine Nachtmusik" via a biaural headphone at 69.4 dB(A) in Leq and 83.6 dB(A) in Lmax. This was undertaken twice with an interval of six days between sessions. Pulse-waves were recorded continuously before, during, and after listening by using a photoelectric plethysmograph. The psychological image each listener had of the music was measured immediately after listening by the SD method composed of fifteen scales with five rating points. The following results were obtained: 1) The pulse-wave height initially became low right after the onset of listening, though the degree of the decrement weakened in the second trial. Spectral analysis of pulse-waves revealed that the power percentage in the low frequency-bands below 0.3912 Hz grew markedly and that in the frequency-bands above 0.4238 Hz it dwindled during and after listening at the first trial. However, these changes of power percentage weakened in the second trial. 2) The image of the music being listened to changed significantly in 11 scales from the first trial to the second trial. 3) Subjects having a previous experience of listening to the music showed smaller image changes and responses in pulse-waves in the second trial than subjects having no such experience. 4) Previous experience of learning any music and the amount of contact with any music were not related to the image changes and pulse-wave responses in the second trial.(ABSTRACT TRUNCATED AT 250 WORDS)