Previous research has implicated the medial prefrontal cortex (mPFC) in the control of classically conditioned autonomic and somatomotor responses. In eyeblink (EB) classical conditioning prefrontal involvement appears to be limited to paradigms that are more difficult to learn, in that acquisition is slower. These include trace conditioning and discrimination/reversal. Some of this research suggests that the participation of mPFC in classical EB conditioning is related to the intensity or type of unconditioned stimulus (US) employed. In the present two experiments we thus studied the effects of manipulation of periorbital shock intensity as the US in Experiment 1 and in Experiment 2 the intensity of a corneal airpuff as the US on Pavlovian trace EB conditioning. The results indicate that there are optimal intensities of both airpuff and periorbital shock as the US in the demonstration of mPFC control of trace classical EB conditioning.