A study was conducted examining serum levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in pulp and paper mill workers. Sera were analyzed from workers from a pulp and paper mill in which a previous evaluation had identified PCDDs and PCDFs in air and surface samples. A total of eight PCDDs and 10 PCDFs were identified in the sera of the workers. Median serum concentrations of PCDDs and PCDFs ranged from 673 parts per trillion (ppt) to 1.9ppt and 19.5ppt to 1.2ppt, respectively, in workers and from 547ppt to 1.8ppt and 15.5ppt to 1.3ppt, respectively, in community resident referents. The median value of four of the eight PCDDs identified was higher in workers with potential for high exposure compared with unexposed referents. Seven workers consistently had the highest values for specific PCDDs and PCDFs. Median and maximum total toxic equivalent (I-TEQ) values were higher in workers classified as having low potential for exposure compared with the high exposure potential group. I-TEQ values were positively related to age, body mass index, and the consumption of locally caught fish and negatively related to current cigarette smoking; however, I-TEQ values were not related to exposure group or duration of exposure. The authors conclude that the serum PCDD and PCDF levels in these pulp and paper mill workers were within the range of those previously reported for individuals without known occupational exposure.