Reports 2 experiments with 32 and 16 male Sprague-Dawley rats assessing the effects of nonreinforced exposure to a tone. In Exp. I, preexposure retarded subsequent conditioning of suppression to that tone, but did not establish conditioned inhibition as measured by a summation test procedure. In Exp. II, preexposure retarded subsequent conditioning of inhibition to the tone. Results are interpreted in terms of reduced stimulus salience resulting from preexposure. (PsycINFO Database Record (c) 2006 APA, all rights reserved)