Poly l.C. an inducer of interferon a. and arecoline. a cholinergic muscarinie agonist, were used as unconditioned stimuli in conjunction with camphor odor to condition the augmentation of natural killer (NK) cell and cytotoxic T lymphocyte (CTL) activities. This observation suggested that two unrelated unconditioned stimuli might be used to associate the signals, and induce mediators at recall that can raise natural killer cell activity. In animals stimulated with an alloantigen to induce CTL. we observed that either poly l:C or arecoline conditioned association, and recall with the same CS raised CTL activity. It appears that conditioning with different substrates can raise either native (NK cell activity) or acquired (CTL activity) immunity. The studies suggest that communication between the CNS and NK cells or CTL appear to take place through a common pathway(s). © 2000, Informa UK Ltd All rights reserved: reproduction in whole or part not permitted. All rights reserved.