Odorants activate an inward current in vertebrate olfactory receptor c
ells. Here it is shown, in receptor cells from the newt, that odorants
can also suppress this current, by a mechanism that is distinct from
inhibition and adaptation. Suppression provides a simple explanation f
or two seemingly unrelated phenomena: the anomalously long latency of
olfactory transduction and the existence of an ''off response'' at the
end of a prolonged stimulus. Suppression may influence the perception
of odorants by masking odorant responses and by sharpening the odoran
t specificities of single cells.