The heats of formation for binary and ternary 3d transition-metal (Ti, V, Fe, and Ni) aluminides are calculated from first principles within the local density approximation. The calculated heats for Ti and Ni aluminides are typically within {approximately}0.02 eV/atom of the experimental values, while the Fe aluminides heats appear to be overestimated by {approximately}0.15 eV/atom. This discrepancy appears to be related to the local density underestimation of the on-site magnetic energy in elemental Fe that enters the alloy heat of formation. The stabilities of selected ternary phases are also discussed, and it is shown that sublattice disorder may stabilize some ternary phases. {copyright} {ital 1998} {ital The American Physical Society}