Tsumura-shuchi-bushi-matsu (TJ-3021) is a processed Aconiti tuber which has a potent antinociceptive action. The present study was undertaken to study the analgesic mechanism produced by TJ-3021. RCS (repeated cold stress) rats in hyperalgesia were markedly suppressed by oral administration of TJ-3021. Intrathecal and intraperitoneal administration of a selective alpha 2-adrenoreceptor antagonist, idazoxan (IDA), reduced significantly the analgesic effect of TJ-3021 in RCS rats. Methysergide (METH), a 5-HT receptor antagonist, demonstrated a similar effect, while intraperitoneal administration of opioid receptor antagonist, naloxone, did not produce the effect. Both oral and intracisternal administration of mesaconitine (MA) which is one of the main potent alkaloids contained in TJ-3021 produced analgesic effect in non-RCS rats.