Transgenic insect-resistant crops produced by combining two or more insect-control traits through conventional breeding are increasingly common in commercial cultivation. In some countries, cultivation of crops with combined insect-control traits may require additional regulatory risk assessments, even though all component traits are approved for cultivation, which requires, among other things, a demonstration that cultivation of the crop poses negligible ecological risk; that is, there is a low probability of harm to non-target organisms. In such situations, cultivation of a crop with the combined traits will also pose negligible ecological risk, provided two hypotheses hold: the potency of the proteins when combined is not greater than when separate; and the exposure of non-target organisms to the proteins is not greater when the traits are combined than when they are separate. The ecological risk assessment for combined traits may be based on tests of these hypotheses, comprising tests for synergism between the proteins in species sensitive to the proteins, and comparisons of protein production in plants with the combined traits and plants with the separate component traits. Tests of these hypotheses are illustrated using Bt11 × MIR604 maize, which produces the insecticidal proteins Cry1Ab and mCry3A. Results from synergism studies using European corn borer and Colorado potato beetle, and from comparisons of the concentrations of Cry1Ab and mCry3A in Bt11 × MIR604, Event Bt11 and Event MIR604 maize, indicate that risks to non-target organisms from the cultivation of Bt11 × MIR604 maize are no greater than from the cultivation of Event Bt11 or Event MIR604 maize.