This report describes the surveillance over the past 8 years of carbon monox ide (CO) levels in a factory producing gas from coal. Where workers were working in areas of the factory where the air might be polluted by CO we found that measurement of carboxyhaemoglobin (HbCO) levels in their blood was a sufficiently sensitive test of exposure. Measurements on samples taken before and after a shift showed a significant difference. Our measurements of a HbCO blank control in two normal population groups was very close to the biological limit value of that for normal groups in the USA and Germany.
