Smoking is one of the most important public health problems of our times. In this paper, we focus on the watching of smoking effect on carboxyhaemoglobin (COHb) and plasma thiocyanate values. The study was accomplished on two groups of blood donors: smokers, 18 men, between 20-51 years old and controls, non-smokers, 10 men, between 22-55 years old. On the blood samples, there have been spectrophotometrically determined: COHb with palladium chloride by microdiffusion method and haemoglobin (Hb) with Drabkin Reagent. The plasmatic thiocyanates were determined spectrophotometrically by Liebig reaction. The data were processed by "t Student" test. The statistical analysis shows that the obtained average values for the COHb from total Hb in smokers (12.51 +/- 10.19) are higher than the average values of the control group (11.45 +/- 10.34). The plasma thiocyanate (mg %) in the smokers' group presents average values of 2.03 +/- 0.58, higher values than those in the control group (1.68 +/- 0.68). From the analysis of the presented results, we notice that the differences between the two groups are statistically non-significantly. These results may be explained by the existence of many factors, which may influence the values of the biotoxicological indicators, among which we mention: passive smoking, the atmospheric pollution in the urban environment, the presence of the chemical noxae at the work place.