The Neurometer is a sensory threshold testing device that has been used to diagnose sensory deficits in humans, but few studies describe its utility in detecting changes in sensory threshold after pharmacological intervention. These studies were done to assess its utility in that capacity in a pre-clinical species. Male Sprague-Dawley rats (200-250 g) were habituated to a tube-type restrainer before testing. A stimulating electrode was placed on the tail and a reference electrode placed on a depilated portion of the flank. The Neurometer outputs current at 2000, 250 and 5 Hz, which are purported to selectively activate Aβ , Aδ , and C-fibers, respectively. For each frequency, current was incremented stepwise from zero until the rat flicked its tail or vocalized. For each frequency this was repeated 5 times, and the three most consistent values were averaged to calculate threshold. Rats were removed from the restrainer and dosed. 1 hour later, they were returned to the restrainer and re-tested. Morphine was tested at 0.3, 1 and 3 mpk (n=6 per group). Thresholds at 0.3 mpk were slightly elevated at all frequencies, but not statistically different from saline. 1 mpk produced elevations of 26%, 52%, and 64% above saline at the 2000 Hz, 250 Hz, and 5 Hz frequencies respectively. 3 mpk produced elevations of 74%, 159% and 81% above saline alone, and these values returned to baseline levels by 4 hours post-dose. Mexiletine at 30 and 60 mpk produced threshold elevations statistically different from vehicle only at the 250 and 5 Hz frequencies. Using the Neurometer we can detect the presence of analgesics that act by distinct mechanisms. Further experiments will be done to determine which classes of analgesics can be detected, and we will determine what doses are required to elevate thresholds, compared to therapeutic or sedative doses.