The effect of neurokinin A (NKA), substance P (SP) and calcitonin gene-related peptide (CGRP) in peripheral hyperalgesia was studied in rats using a modification of the Randall-Selitto paw test. NKA was 10 times more potent than SP which was 500 times more potent than CGRP in inducing hyperalgesia in the rat paw, suggesting that NKA and SP but not CGRP could have an important role in acute hyperalgesic conditions. Furthermore, sensitization induced by several injections of subthreshold doses of NKA or CGRP suggest that these neuropeptides along with SP could participate as mediators or modulators of chronic pain.