First‐principles calculations have been performed for ordered and disordered zinc‐blende Al0.5In0.5N alloys including full relaxation of bond lengths and bond angles. The disordered alloy is predicted to have a mixing enthalpy of +39 meV/atom and a bowing parameter of +2.53 eV at the &Ggr;‐point transition. The similarity of the bulk zinc‐blende and wurtzite &Ggr;‐point transitions also allows an estimate to be made of the energy gap versus composition for wurtzite alloys. In particular, the wurtzite AlInN alloy lattice matched to GaN is predicted to have an energy gap of 5.0 eV. ©1995 American Institute of Physics.