The rat tail flick reflex is a commonly used assay of thermal nociception. Variability in the latency to respond due to the locus of tail heating was examined in spinalized (midthoracic) rats and evaluated retrospectively using data from two previously pubished studies. In all 3 sets of data, a significant relation was found between the proximal-distal site of heating on the tail and the latency of the tail flick reflex. Heating of the most distal sites resulted in shortest response latencies. © 1987.