Carbon dioxide and 1-octen-3-ol were evaluated individually and in combination as black fly attractants. Significantly greater numbers of Cnephia pecuarum were collected in traps baited with CO2 and CO2 + octenol as compared with octenol alone or no bait. While greater numbers of C. pecuarum were collected in traps baited with the combination of CO2 and octenol as opposed to CO2 alone, results were only significantly different (P > or = 0.05) in one test. In contrast, significantly (P > or = 0.05) more adults of Simulium meridionale were collected in traps baited with CO2 alone. Octenol alone was not an effective attractant for the black fly species collected in the course of this study. In addition, use of octenol in conjunction with CO2 may impair representative sampling of black fly species present in a given area.