A screening study was performed on/by essential oils of Nepeta viscida Boiss and Nepeta italica L. using tail-flick and tail immersion (52.5 degrees C) methods, N. italica samples were collected from three different localities of Turkey. Surprisingly, only one of the essential oils showed significant activity, which was blocked by naloxone, indicating the involvement of opioid receptors, This was seen only with the mechanical but not the thermal algesic stimulus, suggesting a specific activity on opioid receptors, excluding mu receptors. The same, active essential oil also exhibited a non-competitive inhibition of acetylcholine contractions of isolated rat ileum but it was inactive on the isolated rat aorta. Furthermore, a correlation between the analgesic activity and the amount of 1,8-cineole was noticed. (C) 1999 John Wiley & Sons, Ltd.