Current 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) concentrations were determined in blood samples for 138 persons who had been involved in assessment, clean-up and demolition activities after the 1953 BASF trichlorophenol reactor accident. From these data and detailed descriptions of the circumstances and duration of individual exposure, a regression model was developed for describing the relationships between various exposure situations and TCDD concentration. The model explained 65% of the variability in log (TCDD) concentration. Using half-life assumptions and the regression model parameters we estimated cumulative TCDD concentrations back-calculated to the time of exposure for all 254 members of the accident cohort. The geometric mean cumulative TCDD concentration for all cohort members averaged 137.7 ppt. Estimated cumulative TCDD concentrations correlated well with chloracne severity. The mean TCDD concentrations were 38.4 ppt for the no chloracne subgroup (n = 139), 420.8 ppt for the moderate chloracne subgroup (n = 59) and 1008 ppt for the severe chloracne subgroup (n = 56). The estimation procedure should be helpful in assessing the relationships between various health outcomes and TCDD exposure in this cohort.