BACKGROUND Methyl bromide (MeBr) is a methylating agent, weak mutagen and possible animal carcinogen. A molecular epidemiological study to examine human exposure to, and consequent DNA damage by MeBr was conducted in an area where this agent is used extensively for soil sterilisation in greenhouses. METHODS During the first part of the study, blood samples were collected from 21 persons within 24 hours after use of MeBr for greenhouse sterilisation, as well as from 19 non-exposed subjects. Personal air sampling was also carried out, indicating mean air concentrations for different subjects in the range 11-78 mg/m3. In the second part of the study, an attempt was made to examine professional applicators of MeBr who suffered particularly high exposures (mean exposures, based on personal monitoring 23-165 mg/m3). The levels of N7-methylguanine and O6-methylguanine, two DNA adducts known to be induced by MeBr, were assessed in blood leukocyte DNA. RESULTS Concerning the first part, two subjects (one exposed and one control) were found to be positive for N7-methylguanine, while none of the blood samples analysed had detectable levels of O6-methylguanine. Among 6 such persons examined during the second part, 2 were found positive for N7-methylguanine while none was positive for O6-methylguanine. CONCLUSIONS Within the detection power of this limited study, no significant evidence of induction of DNA damage in blood leukocyte DNA by MeBr was found.