 several genes involved in the metabolism of carcinogens have been found to be polymorphic in human populations and are associated with increased risk of cancer at some sites . 
 this study focuses on the polymorphic enzyme glutathione transferase mu ( gt mu ) . 
 smokers with low lymphocyte gt mu activity are at an approximately 2-fold higher risk for lung cancer and an approximately 3-fold higher risk for stomach and colon adenocarcinomas . 
 recent cloning and sequencing of the gst1 gene has allowed the development of convenient genotyping methods based on restriction fragment length polymorphisms ( rflp ) or the polymerase chain reaction ( pcr ) . 
 the gst1 polymorphism has been shown to be a deletion of the gene locus . to detect the presence or absence of the gene we amplified exons 4 - 5 and/or exons 6 - 7 of the gst1 gene by pcr . 
 pcr amplification produced bands of 215-bp or 273-bp from individuals with one or two copies of the gst1 allele and no band if the individual was homozygously deleted ( 0/0 ) . in the exon 6 - 7 pcr , we co - amplified a 268-bp portion of the beta - globin gene as an internal reference standard for quantitative analysis of product yield . 
 this allowed homozygote individuals ( + /+ ) to be distinguished from heterozygotes ( + /0 ) . 
 we have compared the gst1 genotype to lymphocyte gt mu activity measured on trans - stilbene oxide ( tso ) in the lymphocytes of 45 individuals . 
 low gt mu activity ( < 67 pmole / min/10(7 ) cells ) was strongly associated ( 24/24 ) with the gst1 0/0 genotype . with the exception of one individual , activities greater than 67 pmole / min/10(7 ) were associated with the presence of the gst1 allele ( 20/21 ) . 
 individuals with the highest gt - tso activity were found to be homozygous for gst1 . 
 ( + /+ ) , while heterozygotes ( + /0 ) generally had lower activity , suggesting a gene dosage effect in lymphocytes.(abstract truncated at 250 words)imagesfigure 2 . 
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