2 experiments offered 8 male Sprague-Dawley rats previously shown to be self-stimulators a choice between signaled and unsignaled brain stimulation (ESB) presented on a variable interval (VI) 1-min schedule in a shuttle box. All Ss consistently chose the signaled side whether the interstimulus interval was .5 or 15.5 sec. Given a choice between unsignaled ESB on 1 side of the shuttle box and no stimuli on the other, 3 of 4 Ss chose the ESB side; the 4th consistently chose the no-stimulus side. On the basis of the data and prior demonstrations that rats prefer signaled to unsignaled painful shock, it is concluded that the preference for signaled over unsignaled reinforcement applies to both the positive and negative case. (15 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)