To evaluate the effect of capsaicin on substance P (SP) expression during induced inflammation in rat pulp tissue.Radioimmunoanalysis was used to measure SP levels in 36 mandibular molar pulps taken from six Wistar rats. Twelve samples were obtained from healthy pulps and used as negative control group. Another 12 samples were obtained after inducing inflammation with mechanical pulp exposure; these were used as the positive control group. Capsaicin was infiltrated into the inferior dental nerve in the experimental group and 12 samples were obtained after mechanical pulp exposure.The lowest SP expression was found in mechanically exposed pulps where capsaicin pretreatment had been carried out (0.028 ng mL(-1)), followed by healthy pulps (0.302 ng mL(-1)). The highest SP expression was found in mechanically exposed pulps with no capsaicin pretreatment (124 ng mL(-1)). The Kruskal-Wallis test showed statistically significant differences between the groups (P < 0.001).Inferior dental nerve infiltration with capsaicin reduces SP expression in dental pulp tissue in rats.