background: to evaluate the influence of gstm1 and gstt1 null genotypes in head and neck carcinogenesis. methods: the frequencies of gstm1 and gstt1 null genotypes were evaluated by multiplex polymerase chain reaction (pcr) in 45 patients with head and neck squamous cell carcinoma and in 45 control group individuals. both groups were composed of smokers paired by gender, age and race. results: the gstt1 null genotype was found in 24.4% of the patients and 17.7% of the control group (p= 0.606), while 44.4% of the patients and 48.8% of the control group were bearers of the gstm1 null genotype (p=0.832). no associations between gstt1 and gstmi null genotypes and primary tumor sites were found. conclusion: in our study, it was impossible to establish the influence of the gstt1 and gstm1 null genotypes in head and neck carcinogenesis.