Monopolar DC-recordings were made of the gross responses from the olfactory bulb of char (Salvelinus alpinus syn. Salmo alpinus L.) and trout (Salmo trutta L.) during stimulation with different odours. The response features studied were: the magnitude and polarity of the slow potential shift, the amplitude of the induced waves and their asymmetrical waveform. Amino acids elicited the largest responses in the lateral part of the bulb. Water containing “crude fish odour” caused the largest responses in the rostral and medial parts. The results demonstrate odour specific differences in the localization of the bulb responses and the separate origin of the slow potential and the induced waves.