Polycrystalline specimens of InAs-In₂Se₃ and InSb-In₂Se₃ alloys have been prepared by suitable annealing of ingots. Measurements have been made of the room temperature values of Hall effect, conductivity, thermoelectric power and infra-red absorption over the whole of the available range of solid solution, and hence values of carrier density n, mobility μ and optical energy gap E_g determined. It is found that the behaviour is similar to that of the corresponding In₂Te₃ alloys in that the alloys rich in A^IIIB^V are n-type and highly degenerate. The observed values of n for the four systems concerned (A^IIIB^V-A₂^IIIB₃^VI) are compared, and possible explanations of the results in terms of solubility of tellurium and selenium in the A^IIIB^V compounds, or the band structure of the A^IIIB^V compounds are discussed. The use of thermoelectric power data to give values of the Fermi level is considered, and it is shown that to give consistent results in the composition range where ionized impurity scattering occurs, a scattering relation of the form τ is proportional to E^+1/2 must be used. The results suggest that the InAs-In₂Se₃ system may show a change in conduction band minimum at a composition of low In₂Se₃ content.