In 1994 samples of bovine milk were taken in 98 sampling points (2 in each of 49 districts of Poland). Levels of organochlorine pesticides and polychlorinated biphenyls (PCB) were determined by capillary gas chromatography. In almost all milk samples DDT and PCB residues were found. Mean concentration of sigma DDT in milk fat was 0.065 mg/kg (from 0.011 mg/kg to 0.382 mg/kg) and PCB 0.017 mg/kg (from 0.007 mg/kg). Other organochlorine pesticides (mainly HCH isomers and HCB) were found in low levels and only in some samples--HCB and gamma-HCB in about 60%, alpha-HCH in 30% of all tested samples. Results of our 20-year study indicate that organochlorine pesticide levels in milk has decreased ten fold during that time.