The use of chlorophenol-containing antistain agents (e.g., Ky5, a wood preservative) ceased in Finland at the end of the 1980s, after 5 decades of use. Exposure of workers to the impurities in these agents (i.e., polychlorinated dibenzo-p-dioxins [PCDDs] and dibenzofurans [PCDFs]) was assessed at three sawmills at which personnel used a sodium chlorophenate product as an antistain agent. Given that compounds accumulate in body fat and their half-lives in humans are long, we could determine 2,3,7,8-substituted PCDDs and PCDFs 5-9 y after the last exposure occurred. We used high-resolution gas chromatography/high-resolution mass spectrometry to determine PCDDs/PCDFs in plasma from 39 Ky5-exposed workers and 18 nonexposed workers. The average total plasma concentration of PCDD/PCDF of the Ky5-exposed workers at the three sawmills were 1018, 945, and 1165 pg/g fat, and corresponding concentrations in the nonexposed workers were 743, 1124, and 844 pg/g fat, respectively. We found no significant differences in total levels between Ky5-exposed workers and nonexposed workers. However, concentrations of the 1,2,3,4,6,7,8-HpCDF isomer were significantly higher (p < .01) among the Ky5-exposed workers at all three sawmills (averages of 224, 99, and 148 pg/g fat) than among their respective nonexposed workers (averages of 43, 48, and 44 pg/g fat). These results indicate that workers had handled Ky5. When we expressed concentration levels in international toxic equivalents (I-TEQs), the mean total I-TEQ PCDD/PCDF of Ky5-exposed workers was significantly lower at one of the sawmills (average = 42 pg I-TEQ/g) than at the other two sawmills (averages of 64 and 62 pg I-TEQ/g)(p < .05). Nevertheless, total concentrations at the sawmills studied were within the range of background levels in the general population.