Among workers employed in factories producing carbon graphite products the risk of cancer due to exposure to polycyclic aromatic hydrocarbons was estimated. In one cohort (plant A), a cancer incidence study was carried out; the number of cases were not significantly increased for lung cancers [7 cases, standardized incidence ratio (SIR) 79] or for cancers of the upper respiratory and alimentary tract (10 cases, SIR 103). In another cohort (plant B), a mortality study was carried out; neither the mortality from lung cancer [13 deaths, standardized mortality ratio (SMR) 118] nor that from upper respiratory and alimentary tract cancers (10 deaths, SMR 125) was significantly higher than expected. Within each cohort, a case-referent study was carried out. In plant A the odds ratios were high but nonsignificant for lung cancers (odds ratio 3.42) and upper respiratory and alimentary tract cancers (odds ratio 2.19) and they showed a nonsignificant relationship with duration of exposure. In plant B, the odds ratios were low for every cancer site.