Studies using HO-1 knockout mice [4, 20, 21] revealed that (i) HO-1-homozygous-knockout (HO-1−/−) mice develop an anemia with accumulation of iron in liver and kidney, (ii) cultured HO-1−/− embryonic fibroblasts produce high free radicals when exposed to hydrogen peroxides, paraquat, or cadmium chloride, (iii) HO-1−/− mice are vulnerable to mortality when challenged with endotoxin, and (ix) HO-1 expression ensures to survive cardiac xenograft. The gene discussed is HMOX1; the disease is anemia (phenotype).