Lymphocyte sister chromatid exchange (SCE) frequencies were determined for 12 long-term coke oven workers and 12 other age-matched steelworkers with no coke oven work exposure. All study participants were nonsmokers. The exposed group had a mean of 28.9 years' exposure to the coke oven emissions. SCE frequencies for the exposed individuals ranged from 7.97 to 11.20 SCEs per cell while the control individuals ranged from 6.73 to 10.60 SCEs per cell. The mean SCE frequency for the exposed group was 9.54 ± SD 1.15 SCEs per cell, and was 14% higher than the 8.35 ± SD 1.09 SCEs per cell of the control group (p = .016). The long-term exposure to coke oven emissions experienced by the coke oven workers may be the explanation for this small difference.