In two fatal cases of aplastic anemia, there was a prolonged indoor exposure to vaporized benzene hexa-chloride (lindane). The chemical was in pellet form and vaporized by electrical warming of a ceramic jacket. The literature was reviewed and although benzene hexa-chloride has been a suspected toxin before, this is, to our knowledge, the first detailed report of benzene hexa-chloride exposure and aplastic anemia in which other suspicious drugs or chemical agents were not used. These two cases allow only a presumptive conclusion to be made. Further repeated observations by others will be necessary to make historical evidence alone sufficient for an etiologic diagnosis. More specific in vitro and in vivo testing procedures are urgently needed to screen the increasingly complex array of drugs to which most of us are exposed. Only in this way can a precise relationship between cause and effect be made.