The relation of olfaction to urination was studied in 14 dogs. A stimulating surface electrode was applied to the nasal mucosa and a recording electrode to each of the external (EUS) and internal (IUS) urethral sphincters. Electrostimulation of the nasal mucosa led to diminished EMG activity of IUS, and effected no change in the response of the EUS. IUS did not respond to stimulation of the anesthetized nasal mucosa. The reproducibility as well as the non-response of IUS to stimulation of the anesthetized nasal mucosa point to the constancy of a reflex relationship between the IUS and nasal mucosa, which we call ''olfactory micturition reflex''. The latency of the reflex (mean ± SD) was 49.2 ± 8.2 ms. It seems that the olfactory micturition reflex induces micturition in the absence of a full bladder. This would explain the repeated successive urination of small amounts of urine, characteristic of dogs, on smelling a uriniferous odor.