In the radiation damage process of austenitic stainless steels, there exists an incubation period before steady-state void growth, and the defect formation behaviors during that period strongly depend on alloy composition. Using the technique of positron annihilation lifetime measurement, the evolution of defect clusters during the incubation period in neutron, electron, and H-ion irradiations was studied for a variety of austenitic stainless steels including commercial and model alloys. The lifetime measurements indicated that in fission neutron irradiation to 0.2 dpa at 363 K, single vacancies were predominantly formed in the commercial alloys, SUS316L and Ti added, modified SUS316, while large voids were formed in Ni and Fe-Cr-Ni. After neutron irradiation at 573 K, stacking fault tetrahedra and/or precipitates were detected in the commercial alloys, while large voids were detected in the model alloys. In the 30 MeV electron irradiation to a dose of 0.012 dpa, the effect of alloying elements on lifetime data was less significant at 353 K, but a significant difference was found between model alloys and commercial alloys at 573 K. The H-ion irradiation at 2 MeV was also performed at room temperature. Defect evolution during the incubation period is discussed on the basis of the neutron, electron and H-ion irradiation results. (C) 2012 Elsevier B.V. All rights reserved.