This research is based on consideration that HbCO sampling, routinely effected on environmental physician demand for workers' biological monitoring, has a low significance. To confirm or reject this statement, we considered two population groups: n. 583 exposed workers and n. 334 not exposed subjects as control group. The habit of smoking (either as number of cigarettes or as time elapsed between the drawn and the last smoked cigarette) was obviously considered on both groups. The results have shown that it isn't possible to acknowledge the effect of a low CO occupational pollution by using HbCO haematic sampling. The A.A. affirm that it's due to low pollution level in work place and to wrong praxis of haematic sampling performed after a long time from the end of working turn. The research showed a direct correlation between HbCO level and smoking habit and a strong association between time elapsed from last smoked cigarette and haematic sampling.