Cytochrome P450 1A(CYP1A)cDNA is used as a probe for evaluation of environmental contaminant.Grass carp(Ctenopharyngodon idellus)liver cell(GCL),kidney cell(CIK),blastula cell(GCB),snout fibroblast cell(PSF)and ovary cell(CO)were exposed to β-naphthoflavone(BNF)to induce CYP1A.The potency of induction was assessed by the ratio of CYP1A cDNA to β-actin(ACT)cDNA derived from semiquantitive PCR.PCR reaction parameters were optimized so that annealing temperature was chosen to be 57 ℃ and cycle to be 30 times.Under such conditions,the CYP1A expression level could be quantitated by Gauss trace ratio of CYP1A/ACT. PCR amplification product of ACT and CYP1A cDNA showed that CYP1A expression level was very low in control grass carp cells while increased in BNFtreated cells significantly.The expression level of CYP1A in BNFtreated GCL,CIK and CO cells had significant difference(P<0.05),which was sorted as GCL>CIK>CO.But that of GCB or PSF cell could not yet be detected.The state of CYP1A expression in grass carp cells was similar to homologous tissues,and the level in homologous tissues of BNFtreated grass carps was sorted as liver>kidney>ovary.The results indicated CYP1A expression level in vitro had certain correlation with that in vivo.This study illustrates the high potential of fish cell lines in ecotoxicology.