Mortality in 1422 male carbon black process workers with at least 12 months exposure was recorded from 1947 to 1980. Excess deaths from lung cancer, which were not statistically significant, were observed but interpretation is complicated by the incompleteness of data on the populations from two of the five factories studied. The highest excesses of lung cancer were in the two factories with incomplete data, which also had the lowest measured dust levels (though these were high). Furthermore, the duration of employment of lung cancer decedents was slightly less than for individually matched internal controls. Excess lung cancer after the tenth anniversaries of first exposure was 10 observed, 5.1 expected for the two factories with incomplete data; and 11 observed, 7.9 expected, for the other three factories.