Olfactory research is entering a new phase, in which molecular mechanisms are being revealed that go considerably beyond traditional concepts. New ways of characterizing these mechanisms are needed, and some suggestions toward that goal have been made in this review. These suggestions recognize that, whereas formerly our terms and concepts regarding olfactory stimulus-response characteristics came mainly from organic chemists and psychophysicists, the main impetus at present comes from molecular biology. A desirable terminology, therefore, is one that is familiar to molecular biologists and can facilitate comparisons with other systems--immune, endocrine, nervous--where similar methods and terms are in use. The suggestions made here for the olfactory system could also be adapted for the taste system. Taste stimulation could be characterized, for example, in terms of gustagens interacting with G-cell receptors, stimulation being determined by the gustatope of a particular ion or molecule. It should be emphasized that such terms and mechanisms may not need to be invoked in studies at behavioral or psychophysical levels. However, the need for them at the receptor level may well be an accurate reflection of our progress in applying methods of molecular biology to these systems.