Lung cancers occurred at a higher rate among workers who had been potentially exposed in the past to chloromethyl-methyl- ether/bis-chloromethyl-ether than among unexposed workers at the same plant (RR 4.4, 95%Cl 1.8-10.9), or among an externalreference population (RR 4.4, 95%CI 5.5-10). The average age at diagnosis among the exposed was at least 10.5 years lower than among theunexposed. The predominantly small-cell cancers of the exposed were mostly oat-cell, a characteristic of lung cancers in groups exposed to CMME/BCME. There was a positive dose response. The mean time from first exposure to diagnosis was 13 years (95%CI 8-18 years). Dose and induction time were not associated. The rate for the exposed workers peaked somewhere between 7 and 13 years after the start-up of the process, and has declined since. It is impossible to say if the period of excess rate has passed completely, but there are indications that it is essentially over.