A study on the hazards of lead on environmentally exposed 80 male petrol station attendants and 35 male University students (who are residents of Abeokuta, an urban city in Nigeria) has been investigated by spectrophotometric analysis of their blood with 5,5 – dithiobis (2–nitrobenzoic acid) (DTNB) at 412 nm, pH 7.4 and at 370C. DTNB permits the determination of sulfhydryl groups in simple compounds and has been used to monitor the disappearance of free SH groups in hemoglobin (Hb). The concentration of lead in the blood of each sample was also determined. The concentration values ranged from for the petrol station attendants 21.40 to 70.51 μg/dl and 14.23 to 17.65 μg/dl for the University students who served as the control. The mean values of blood lead concentration were found to be 41.36±2.71μg/dl for petrol station attendants, while that of the control is 14.31±2.16μg/dl. The mean blood lead values of the petrol station attendants were significantly higher than that of the control (P< 0.05). At 370C, the lead-hemoglobin reacted with DTNB resulting in decrease in the number of sulfhydryl group (ß93 –SH) per hemoglobin molecule. The values range from 3.8 to 5.6 -SH groups for the petrol attendants and 4.6 – 5.8 -SH groups per tetramer for the control. The mean values are 4.8±1.67 –SH and 5.5±2.40 groups per Hb molecule for the petrol station attendants and the University students (control) respectively. This study demonstrates a predominant elevated blood lead levels in petrol station attendants in Abeokuta City, Nigeria and that atmospheric lead represents a significant source of human exposure to environmental pollutants in any city. These results also show differences in the reactivity of sulfhydryl groups in the hemoglobin of this subject population. It is suggested that these differences arise from the variations in the level of exposure to lead, the environment of their ß93 sites, age, drinking and feeding habit, smoking status, as well as the level of education of the subject.s.s