A retrospective mortality study has been carried out on workers employed in the manufacture of chlordane and heptachlor between 1946 and 1976. The study group was comprised of 1403 white males who worked for more than three months at either of the two plants in the United States now producing these compounds. Information on deaths among terminated employees was obtained from the Social Security Administration and supplemented by information collected by another investigator by individual follow-up. There were 113 deaths observed in the group, compared to 157 expected, giving a standardized mortality ratio (SMR) of 72. There was no overall excess of deaths from cancer, even among workers followed twenty or more years after entry into the occupation. There was one death from liver cancer. An excess of deaths from lung cancer (12 observed, 9.0 expected) was not statistically significant and was not distributed by duration of exposure or of latency in any pattern suggesting an etiologic role for chlordane-heptachlor exposure. Although diseases of the circulatory system as a whole showed fewer deaths than expected (SMR 83), there was a statistically significant excess of deaths from cerebrovascular disease (17 observed, 9.3 expected). This excess was not related to duration of exposure or latency and occurred exclusively after termination of employment.