Event MIR604 maize expresses a modified Cry3A protein (mCry3A), for control of corn rootworm. As part of the environmental safety assessment of MIR604 maize, risks to non-target organisms of mCry3A were assessed. The potential exposure of non-target organisms to mCry3A following cultivation of MIR604 maize was determined, and the hypothesis that such exposure is not harmful was tested. The hypothesis was tested rigorously by making worst-case or highly conservative assumptions about exposure, along with laboratory testing for hazards using species taxonomically related to the target pest and species expected to have high exposure to mCry3A, or both. Further rigour was introduced by study designs incorporating long exposures and measurements of sensitive endpoints. No adverse effects were observed in any study, and in most cases exposure to mCry3A in the study was higher than the worst-case expected exposure. In all cases, exposure in the study was higher than realistic, but still conservative, estimates of exposure. These results indicate minimal risk of MIR604 maize to non-target organisms.