The objective of this study was to study was to compare chromium (Cr), nickel-chromium (Ni-Cr), and control groups for sister chromatid exchange (SCE) in lymphocytes to obtain an understanding of the mutagenic effect of Cr(VI) in humans. Subjects totaled 91 persons from the 3 groups, including 14 Cr and 34 Ni-Cr electroplating workers and 43 control group members. Results showed that blood and urine Cr concentrations were highest among Cr workers (11.39 microg/l, 14.7 microg/g creatinine), next highest among Ni-Cr workers (5.28 microg/l, 6.2 microg/g creatinine), and lowest among the control group (2.36 microg/l, NA). After adjustment for smoking habits, SCE/cell values were 10.6, 9.4, and 8.3 for Cr workers, Ni-Cr workers, and controls, respectively. A synergetic effect was shown on HFC (high-frequency cells) percentages for Cr workers who also smoked. Odds ratios were 31.78 and 3.66 that Cr and Ni-Cr workers would have higher HFC percentages than the control group, respectively. The authors conclude that SCE in lymphocytes is useful for evaluation of the biological effects of environmental mutagens.