We have detected, by the use of a bio-assay system, a naloxone-like activity (NLA) in whole, unfractionated venoms from the following varieties of bees: Vespula pennsylvania, Vespula germanica, Vespula maculifrons, Polistes annularis, Dolichovespular maculata and Vespa craboro. We have been able to exclude some of the known autacoids that could mimic jthe effect of naloxone in our bioassay system.