The mechanical properties and microstructures of Type-304 stainless steel were studied as a function of cold work, neutron irradiation, and testing temperature. True-stress, true-strain tensile tests were made on nonirradiated specimens at 70°F (21°C), 600°F (315°C), and 1300°F (700°C), and on irradiated specimens at 70°F and 600°F. Specimens were irradiated to 1.25 x 1020 n/cm2 (>1 MeV) at 110°F (43°C). Neutron irradiation increased the yield strength and ultimate tensile strength of annealed and cold-worked specimens at 70° F and at 600° F. The incremental increase in these properties decreased with increasing cold work. The elongation of nonirradiated and irradiated specimens tested at 70° F was found to increase with initial levels of cold work and then to decrease. This effect was not observed at 600° F. The most severe decreases in mechanical stability were observed in heavily deformed (greater than 20% reduction in thickness) and irradiated specimens tested at 600° F. These specimens failed in a ductile manner with total elongations as low as 1/2%. The increases in the strength and decreases in plastic stability produced by irradiation were combined by measuring the energy absorbed to plastic instability (area under the true-stress, true-strain curve up to the point of maximum load). This energy value was found to be an effective method for comparing the effects of the various variables. Cold work was found to produce large amounts of austenite-to-martensite transformation. Neutron irradiation was found to produce no measurable increase in martensite content. Transmission electron microscopy of irradiated specimens confirmed the presence of martensite and epsilon phase in Type-304 stainless steel. Irradiated specimens contained high concentrations of black dots which were not observed in nonirradiated specimens. In some instances these black dots could be resolved into loops. These black dots are presumed to be clusters of vacancies or interstitials produced by neutron radiation.