Results: Comparisons between the results of all groups revealed that: folate and vitamin B₁₂ were lower and homocysteine was higher in gamma irradiated malignant and gamma irradiated nonmalignant mice in comparison with normal control and malignant mice. Folate and vitamin B₁₂ levels were also lower whereas homocysteine was higher in malignant mice in comparison with normal control   group. Conclusion: These results denoted that increased homocysteine or/and decreased folate and vitamin B₁₂ in the two malignant exposed groups may have a role in the primary tumor regression leading to the recommendation that preventing up taking of folate and vitamin B₁₂ either as supplements of land nutrients rich with subsequent increase in homocystein may be beneficial through its toxic effect in stopping or minimizing tumor progression. The disturbance of vitamins may be due to the metabolic alterations associated with tumor development.