An attempt is made to interpret the solid solution hardening of Ni₃Al alloys in terms of the elastic interaction between the strain fields of a dislocation and a solute. Ternary additions are made to the L1₂ intermetallic compound with both B-subgroup and transition metal elements which substitute for Al-sites. Young’s modulus of the ternary alloys is measured and the rate of change in elastic constant per one atomic per cent of solute (dE⁄dc) is determined. With the available data for the rate of solution hardening (dσ⁄dc) and the rate of change in lattice constant (da⁄dc), analyses are made on the relation between dσ⁄dc and combined parameters. It is found that the solution hardening is best described by a combined parameter appropriate for the elastic interaction involving edge dislocations, where atomic size misfit plays a major role and the contribution of modulus misfit is minimal. However, the correlation between dσ⁄dc and the combined parameter splits into two curves, one being for transition metal elements and the other for B-subgroup elements. It is found that for the additions of transition metal elements there is an extra hardening over what is expected from the treatment on B-subgroup elements.