Additives in petroleum solvents have been reported to have adverse health implications. An evaluation study on some toxicological effects of occupational exposure to petroleum products (especially petrol which contains tetraethyl lead) amongst twenty five occupationally exposed artisans and twenty five graduate students of College of Health Sciences, Nnamdi Azikiwe University, Nnewi, Nigeria as controls, was carried out using the following biochemical markers: electrolytes, urea, uric acid, inorganic phosphorus, creatinine, zinc and blood lead, as well as the activities of alanine and aspartate aminotransferases, and alkaline phosphatase. The results showed that occupational exposure of human subjects to lead in petrol increases the concentrations of uric acid (357 ± 123μ mol/L) and phosphate (1.5 ± 0.5m mol/L) in exposed subjects compared with unexposed subjects (uric acid 228 ± 105μ mol/L, phosphate 1.2 ± 0.41m mol/L; p < 0.01 in both cases). Significantly lower activities were observed for alkaline phosphatase (66 ± 18.9 iu/L). The activities of alanine aminotransferase (11.4 ± 4.0 iu/L) and aspartate aminotransferase (15.8 ± 4.4 iu/L) in occupationally exposed artisans were higher compared with unexposed subjects (alkaline phosphatase = 78 ± 22.4 iu/L alanine aminotranferase = 6.8 ± 2.7 iu/L, aspartate aminotranferase = 9.6 ± 3.5i u/L; p < 0.01 in all cases). Occupational exposure of human subjects to lead significantly increased blood lead (59.6 ± 15.9 μg/dL) and decreased plasma zinc (71.3 ± 14.4 μg/L) in exposed compared with unexposed subjects (blood lead = 35 ± 7 μg/dL, zinc = 108.4 ± 16.9 μg/dL; p < 0.01). The results indicate that occupational exposure to lead in petrol may compromise liver and renal function.