A dilution type of olfactometer was designed to bring a known quantity of odorous substance (in mg per liter) into the nostrils of rabbits. Electronic integrator units were added to each channel of a 4-channel grass electroencephalograph. The integrated spike discharges from 4 points on the olfactory bulb were then measured as a function of the concentration of amyl acetate, heptane, ethyl ether, and benzene. Discharge strength and duration increased approximately as negatively accelerated functions of concentration. The curves reached their asymptotes in about 1-1.5 log units of physical concentration. This rapid rise might be related to the apparently poor intensity discrimination of olfaction. The response curves, in terms of milligrams per liter, were arranged in the following order: amyl acetate, heptane, benzene, and ether. A bulbar antero-postero spatial differentiation was confirmed although it was quite gross. Amyl acetate lost effectiveness as a stimulant relative to heptane from front to rear. Ether elicited a spatial pattern of discharge similar to that of heptane. Benzene yielded no consistent pattern and elicited the smallest responses. These relationships held at all concentrations. Temporal differentiation of the discharge elicited by the various chemicals was also confirmed. Electrode depth in the spike layers did not affect the spatial, temporal, and concentration relationships. The spatial and temporal differentiation observed was not considered to provide an adequate basis for olfactory quality discrimination.