Reports 3 experiments employing a conditioned-suppression procedure with male Sprague-Dawley rats (N = 76). In Exp. I and II, initial fear conditioning with a noise UCS was followed by habituation of that UCS. Subsequent testing showed that UCS habituation attenuated the previously established conditioned response. In Exp. III UCS habituation followed the establishment of both a 1st- and a 2nd-order conditioned response. Habituation attenuated the response to the 1st-order, but not to the 2nd-order, stimulus. Implications are noted for the nature of 1st- and 2nd-order conditioning. (PsycINFO Database Record (c) 2006 APA, all rights reserved)