The yield stress dependence on grain size and solute content in preannealed and also in quenched polycrystalline α-CuAl alloys was measured. It was found that the Hall-Petch relation is valid for all the alloys in the two conditions. Preannealed materials, which are characterized by the presence of ordered domains, exhibit higher yield stresses as a function of the inverse square root of the grain size arising from larger values of both the intercept σ0 and the Hall-Petch slope ky. As the alloys become more concentrated, the differences δky and Δσ0 between the preannealed and the quenched specimens increase for the same aluminium content. These results are interpreted in terms of the yield stress contribution of the ordered particles, in conjuction with the influence of the amount of solute segreration to grain boundaries on the slope value. It is concluded that δky > 0 is not the reflection of an interactive effect between grains and domains but is rather a consequence of the allowance of a higher grain boundary solute concentration in the ordered condition. Owing to the large domain volume fractions of the alloys having larger aluminium contents, the actual contribution to the yield stress of disperse order was evaluated taking into account matrix depletion effects. In order to accomplish this, domain sizes and volume fractions were determined through microcalorimetric dissolution kinetics studies using current theories on solute hardening. It was also estimated that the contribution of quenched-in vacancies to the yield stress was neglible at room temperature in all cases.