OBJECTIVE:　To　investigate　the　application　of　293　cells　to　detect　suspected　carcinogens　and　provide　experimental　evidence　by　using　in　vitro　cell　transformation　assay　and　tumorigenicity　study.　METHODS:　The　transformation　systems　of　cells　cultured　in　vitro　have　been　adopted　to　clarify　the　tumor　promotive　activity　of　Microcystin　LR　(MC-LR).　The　malignant　transformation　of　293　cells　induced　by　MC-LR　is　tested　by　several　methods　including　clone　forming　in　soft　agarose,　serum　requirement　assay　and　tumor　forming　in　mice　to　define　the　promotive　activity　of　293　cells.　RESULTS:　293　cell　acted　like　tumor　cells　after　induced　by　MC-LR:　serum　dependence　decreased,　anchorage　independence　growth　in　soft　agarose　and　formed　cell　clones,　malignant　tumors　appeared　in　SCID　mice.　CONCLUSION:　293　cells　were　easy　to　culture　and　sensitive　to　environmental　carcinogens　so　that　can　be　used　in　detection　of　suspicious　carcinogens.