Ab　initio　computations　were　carried　out　at　MP2/6-311+G(d,p)　level　to　study　the　mechanism　of　the　formation　of　DNA　alkylation　agents　from　the　metabolism　of　3,5-dimethyl-1-nitrosopiperazine　(DMNP)　and　its　derivatives.　The　influence　of　the　substituent　groups　of　the　N＇　atom　was　investigated　in　the　formation　of　the　two　alkylation　centers　on　the　alpha-　and　gamma-positions　of　the　DMNP　metabolites.　The　relationship　between　the　formational　activities　of　the　two　active　centers　and　the　carcinogenic　potency　of　the　parent　compounds　was　also　explained.　The　results　show　that　the　parent　compounds　are　inclined　to　exhibit　higher　carcinogenic　activity　when　their　alpha-position　and　gamma-position　metabolites　are　easier　to　produce　the　active　electrophilic　intermediates.　However,　if　one　alkylation　center　is　blocked,　the　carcinogenic　potency　of　the　compounds　is　decreased　obviously.　Therefore,　the　carcinogenecity　of　DMNP　was　supposed　to　depend　on　the　synergetic　alkylation　of　the　alpha-　and　the　gamma-positions.　It　is　necessary　to　consider　the　alkylating　activity　of　these　two　alkylation　centers　and　the　relationship　between　them　in　the　appraisement　of　the　carcinogenecity　of　DMNP.