Polychlorinated biphenyls (PCB) were manufactured between 1929 and 1989. Due to their great chemical persistence, these substances have been used for many different purposes. These chemical properties, however, caused PCB to accumulate in the food chain and resulted in background exposure of the general population. PCB has also been used as plasticizer for sealants in prefabricated buildings, thus causing problems to the present date. At the end of the 90-ties in a school in Nuremberg, Germany, elevated PCB concentrations were measured in indoor air. Some of these results were higher than 3,000 ng/m(3) which means decontamination according to the German "PCB directive". Press coverage made these results a matter of public debate, so that teachers, school children and parents were highly worried because of possible health effects. The Bavarian Minister for Health, Nutrition and Consumer Protection asked us to examine school children and teachers with regard to their internal PCB exposure and health complaints. A group of school children from a non-contaminated school served as controls. For the determination of PCB levels the plasma samples were blinded before analysis. Lower chlorinated PCB (PCB 28, 52, 101) were detected more often and in higher concentrations in plasma samples of school children of the contaminated school compared to the controls. The plasma levels of the higher chlorinated PCBs (PCB 138, 153, 180) did not show similar differences between exposed and non-exposed school children. The relative PCB doses additionally taken up in the contaminated school were less then 5 % of the background exposure of the children. That is why it could finally be concluded that no appreciable additional health risk may result from inhalation of PCB contaminated indoor air in this school. Due to the design, performance and interpretation of this study, including representatives of parents and teachers, these results were widely accepted by most of the parents who initially had been very concerned about possible health effects.