Relative independent mutations induced by vehicle (A), DEB (B), BSO/DEB (C), or O6-BzGua/DEB (D) in livers of Big Blue® transgenic mice. O6-BzGua (80 mg/kg, ip) was administered 1 h prior to treatment with DEB (25 mg/kg, ip) and BSO (8 mg/kg, ip) was administered 2 h prior to treatment with DEB (25 mg/kg, ip). Transition mutations (■); transversion mutations (□); frameshifts and others (diagonal shading). The P values are for comparison of the AT to GC transversions between Parts A and B (P <0.0001), between Parts B ad C ((P <0.02) and between Parts B and C (P <0.05).