Power spectral analysis and digital filtering of brain stem auditory evoked potentials (BAEP) were performed in dogs. The BAEP were recorded in 7 dogs, using alternating clicks at frequency of 20 Hz. The clicks were delivered monaurally at intensity of 90-dB normal hearing level. Power spectral analysis indicated that the frequency compositions of the averaged responses were divisible into 4 frequency bands: A (30 to 390 Hz), B (390 to 680 Hz), C (680 to 910 Hz) and D (910 to 1960 Hz). The frequency limits of digital high-pass (HP) and low-pass (LP) filters, at which neither peak-to-peak nor absolute amplitudes were reduced, were 1,170 and 1,270 Hz for P1, 290 and 1,170 Hz for P2, 290 and 980 Hz for P3, 290 and 980 Hz for P4, and 200 and 880 Hz for P5, respectively. The dual structure of BAEP was confirmed in dogs. Below 200 Hz for the HP filter, peak-to-peak and absolute amplitudes of afl waves were not significantly reduced. Therefore, this frequency may be a boundary frequency between low- and high-frequency components of BAEP in dogs. The main source for the high- frequency components that constituted each positive peak and the following trough was derived from frequency bands C and D. The frequency limits of 200 Hz for a digital HP filter and of 1,270 Hz for a digital Lp filter, at which amplitudes of aU waves were not reduced, support the analog filter settings recommended for dogs (ie, less than and qual to 53 and 3,000 Hz for analog HP and LP filters, respectively).