One hundred and twenty-two persons employed in an industrial waste incineration plant were examined with respect to organic and inorganic substances which may be produced during the combustion of different waste. The employees were divided into three groups: persons with contact with the incinerator (WI workers, n = 45), periphery workers (n = 54) and management (n = 23). For the evaluation of internal exposure, the levels of lead, cadmium, mercury, benzene, toluene, ethylbenzene and m-xylene in blood, chromium in the erythrocytes, polychlorinated biphenyls, hexachlorobenzene and pentachlorophenol in plasma, and arsenic, chromium, nickel, vanadium, chlorophenols and hydroxypyrene in urine were determined. The internal exposures of the three groups were tested against each other and were compared with the reference values of the general population. Differences between the groups investigated were tested using the U test according to Wilcoxon, Mann and Whitney (P < 0.05). The biological exposure limits valid in Germany (BAT values) were not exceeded in any cases. Compared with the background levels of the German population, certain parameters were exceeded in several employees. Significantly higher levels of the WI workers in comparison to both periphery workers and management were found for toluene in blood (median: 1.1 vs 0.9 vs 0.6 microgram/l). For the lead and cadmium levels in blood and for the urinary excretion of arsenic, 2,4-dichlorophenol and tetrachlorophenols, statistical differences were found only between WI workers and one of the other groups. However, in all cases the elevations were very small and of interest more from the environmental than from the occupational point of view. It must be stressed that this waste incineration plant is very modern in terms of worker health and safety. At older plants without corresponding health and safety measures, higher internal exposure of the employees to hazardous substances may exist.