The development of industry brings an increase in number of industrial poisonings by carbon monoxide. To treat these the East-Slovakian Ironworks has organised preventive measures. Instructive cases are illustrated. Measurement of carbon monoxide--haemoglobin in the laboratory gives an objective index for the degree of poisoning and the progress of treatment. The authors used cobaltous nitrate (0.13 mol/l) for control of the method. The best treatment was found to be hyperbaric oxygen in combination with multi-vitamin treatment. In some cases cardiorespiratory and antibiotic treatment is also necessary.