The lower inhibitory effect of allyl sulfides on benzo[a]pyrene (B[a]P)-induced toxicity in a cell culture model, rather than in an animal model, was related to their volatile natures. An improved assay system for these volatile chemicals is now suggested. When hydroxypropyl-beta -cyclodextrin was used as an inclusion vehicle of sulfur chemicals, cell viabilities of B[a]P-treated cells were significantly increased by 30-100% and 30-80% at 100-1000 muM diallyl disulfide (DADS) and 10-100 muM diallyl trisulfide (DATS) treatments, respectively.