The protein content of insect venoms was determined using a Coomassie blue dye binding assay as well as the Lowry phenol assay. The Lowry method tended to give excessively high values with many of the venoms because of the presence of low molecular weight phenolic compounds and other interfering substances. Using the dye binding method honey bee stings were found to contain 59 +/- 7 micrograms of protein, bumblebee and carpenter bee stings from 10 to 31 micrograms, yellow jacket stings from 1.7 to 3.1 micrograms, white faced hornet stings 2.4 to 5.0 micrograms and paper wasp stings from 4.2 to 17 micrograms protein. This is in good agreement with the value of 50 micrograms previously estimated for honey bee stings and is the first reported data for the other species.