Concentrations of chlorinated hydrocarbons and polychlorinated biphenyls (PCB) were determined by capillary column gas chromatography in samples of bone marrow from 38 children with leukaemia (16 samples/pools) and 15 control (5 pools). The highest mean and median concentrations were detected for total PCB (mean = 3.568 mg/kg fat basis/median 2.904 mg/kg) followed by the sum of the dichlorodiphenyltrichloroethane metabolites (1.775/1.059 mg/kg), hexachlorobenzene 0.354/0.260 mg/kg), the sum of the hexachlorocyclohexane isomers (0.133/0.093 mg/kg) and dieldrin (0.109/0.063 mg/kg). The CHC and PCB concentrations in bone marrow were two- to threefold higher than in fat tissue. Comparing children with and without leukaemia similar concentrations of CHC and PCB were found.