OBJECTIVE: To evaluate changes of auditory brainstem response (ABR) and its role in monitoring auditory functions during the brainstem surgery. METHODS: The data of 400 ABRs from 5 operations for removal of astrocytic glioma, cavernomas or dermoid from the brainstem were analyzed. The changes in latencies, amplitudes and wavefroms were dynamically observed and statistically analyzed with t test and Factor analysis. RESULTS: Surgical manipulations, such as stretching, separation and extrusion, induced the prolongation of ABR peaks and interpeak latencies of waves I, III, V. The amplitudes of waves decreased. Three out of 5 cases presented reversible changes in latencies and wave forms. The dynamical analysis showed: The maximal variable range of latency(LMVD) was more than 11.30%, the maximal reversible degree of latency(LMRD) was more than 53.85%, the time of convalescent half-value latency(LCHT) was around 8-40 min, AMVD was more than 40%, the AMRD was more than 200%, and the ACHT was around 5-40 min. In 2 out of the 5 patients the postoperative ABR latencies kept prolonged, some postoperative waves were malformed and difficult to be identified, One case died, another lost consciousness, their LMRDs were less than 33.33%. These findings suggested that surgical intervention had significant effects on the ABR latency (P < 0.01). CONCLUSION: ABR offers a promise for sensitive detection of the brainstem function. Its latency, amplitude and waveform show us dynamic changes of the brainstem status and can be used as an index during the operation on the brainstem and its adjacent region.