Serpinb3a−/− bone marrow stromal cells have increased antioxidant stores compared to Balb/c bone marrow stromal cells. Antioxidant stores were determined in Sepinb3a−/− and Serpinb3a+/+ Balb/c bone marrow cells that received 5 or 10 Gy irradiation based on data with other bone marrow stromal cell lines in other experiments (10, 11), and reflecting a dose on the linear portion of the survival curve and a 100% lethal dose, respectively. Cells were harvested at 0, 1, 3, 5 and 18 h postirradiation. Antioxidant stores were measured in Serpinb3a−/− compared to Serpinb3a+/+ Balb/c bone marrow stromal cell lines in vitro. Total antioxidant stores were increased at baseline in Serpinb3a−/− compared to Serpinb3a+/+ Balb/c bone marrow stromal cell lines. Antioxidant store levels remained elevated in Serpinb3a−/− stromal cell lines after 5 or 10 Gy irradiation. (n = 3 per data point). *P < 0.05 compared to 0 h of respective strain; #P < 0.05 compared to Serpinb3a+/+ Balb/c background at the same time.