Arylalkynes such as 4-phenyl-1-butyne (PBY), 5-phenyl-1-pentyne (PPY) and 2-ethynylnaphthalene (2-EN) are suicide inhibitors of cytochrome P450 enzymes. Arylalkyl isothiocyanates such as 6-phenylhexyl isothiocyanate (PHITC) are structurally related to arylalkynes and are known to inhibit the cytochrome P450 mediated metabolic activation and tumorigenicity of a tobacco-specific lung carcinogen, 4-(methylnitrosamino)-1-(3-pyridyI)-1-butanone (NNK). In this study, we compared the ability of PBY, PPY, 2-EN and PHTTC to inhibit A/J mouse lung tumorigenesis by NNK. Groups of 20 female mice were gavaged with 5μmol of arylalkyne or PHTTC in corn oil. Two hours later they were given a single i.p. injection of 10 μmol NNK. The mice were killed 16 weeks later. PPY and PHlTC were both potent inhibitors of tumorigenesis by NNK, reducing lung tumor multiplicity from 8.35 tumors per mouse to 0.40 and 0.35 respectively. PBY and 2-EN also significantly inhibited tumor multiplicity. The results of this study demonstrate that arylalkynes and PHITC are potent inhibitors of NNK induced lung tumorigenesis in A/J mice, consistent with the hypothesis that inhibition of specific cytochrome P450 enzymes is involved in inhibition of tumorigenesis.