Grasshoppers (Orthoptera) were collected in pastures that had been sprayed with malathion and acephate to estimate the secondary exposure of insectivorous birds to these pesticides. Residues of malathion were below 3 ppm at 30 'and 54 hours after spraying and no malaoxon was detected. In contrast, acephate was found at 8 and 9 ppm 4 hours after spray; 3-5 ppm of the toxic metabolite methamidophos were also detected at that time. By 53 hours postspray, acephate levels declined to 2 ppm and methamidophos to less than 1 ppm. These results suggest that although malathion may not be a hazard to insectivorous species. acephate may be hazardous through metabolic transformation to methamidophos.