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Following a previously published report on an investigation into the pharmacokinetics of 13C-labelled polychlorinated dibenzo-p-dioxins and dibenzofurans administered orally as a bolus to lactating cows, the present report describes the elimination kinetics of unlabelled dioxins ingested by the same cows while being kept in contaminated pastures in the Lickebaert-area. A control animal not knwon to be exposed to dioxins in excess of background levels showed dioxin concentrations in milk and subcutaneous fat as expected except for two congeners indicating a possible accidental exposure to pentachlorophenol. From the dioxin concentrations in milk and subcutaneous fat of the Lickebaert cows half lifes could be calculated for nine congeners. In general the elimination half lifes as judged from milk concentrations appeared to be longer (45-110 d) than found previously for labelled dioxins. This phenomenon was most striking for the higher substituted congeners. The values found for the TEQ-dominating congeners did not differ essentially from those found before. In subcutaneous fat half lifes appeared to be shorter (25-40 d) than those derived from milk data. The discrepancies between the milk and subcutaneous fat data observed here and between the present results and those reported previously may be due to physiologic and kinetic processes occurring in the lactating cow.