Immunological examinations were done in 30 fattening pigs from three swine farms (D., M., T.) and 20 dairy cows from one cattle farm (N.) in the district of Hodonín in 1994. At the same time, samples of stable dust deposits collected in the four farms were analysed for the contents of mercury, cadmium, lead, gamma-HCH (lindane), and total DDT and polychlorinated biphenyls (PCB). Decreased blood level of lysozyme (0.92 mg/l) was found in the swine herd D. Ten percent of the pigs in the herd were affected with purulent skin lesions. The concentrations of the pollutants under study in the dust deposits collected in the herd D. were low. An increased concentration of PCB (0.263 mg/kg) in stable dust but no adverse effects on the immune system were found in the swine herd M. Eosinophilia (6.2%), increased extensity of Ascaris suum infection (25%) and a high content of lead in stable dust (11.2 mg/kg) were typical of the swine herd T. A high content of lindane (0.139 mg/kg) and an extremely high content of lead (214 mg/kg), which can participate in the immunosuppression of lymphocytes, were found in the cattle herd N. The activity of lymphocytes was depressed in 35% of the cows and the mean value was at the lower limit of the physiological range. Hazardous pollutants can affect the immune system of farm animals and their penetration into the stable environment should be prevented.