A549 cells expressing hMYH demonstrated increased survival after exposure to conditions with elevated levels of oxygen compared to cells expressing only the pSF91.1 vector ( Figure 5A ). Results were highly significant at all time points except after 12 hours O 2 where it almost reached a highly significant value. The differences between pSF91.1 and hMYH varied from 12% after 12 hours O 2 exposure to 7% after 72 hours O 2 exposure. A549 cells expressing hMYH also demonstrated increased survival after exposure to all doses of radiation in comparison to pSF91.1 ( Figure 5B ). These results were also highly significant at all doses of radiation except at 250 Rads where it almost reached a highly significant value. The differences between pSF91.1 and hMYH varied from 12%-14% for all doses of radiation. Also noted in these experiments was that vector control cells demonstrated no Experiments looking at the effects of H 2 O 2 on cells expressing the repair genes did not demonstrate increased survival for any of these repair genes when compared to vector control cells ( Figure 5C ). This data demonstrates that over-expression of hMYH has the ability to improve cellular survival under conditions of hyperoxia and radiation but may not be able to overcome the toxicity of H 2 O 2 .