In　this　paper,　we　consider　a　nonautonomous　competitive　Lotka-Volterra　system　of　two　species　with　the　effect　of　toxic　substances.　It　is　shown　that　toxic　substances　play　an　important　role　in　the　extinction　of　species.　We　prove　that　one　of　components　will　be　driven　to　extinction　while　the　other　will　stabilize　at　a　certain　solution　of　a　logistic　equation　under　some　conditions.　(c)　2006　Elsevier　Inc.　All　rights　reserved.