The Haematotoxic implications of exposure to petroleum fumes through inhalation in human subjects were investigated. A total of 400 subjects (200 males and 200 females) aged between 18-30 years participated. Each gender was further categorized into two groups of 100 each for control and test, respectively. The test group was again subdivided into test 1 (T1) and test 2 (T2) in both sexes. T1 subjects were exposed to petroleum fumes for two years and below while T2 subjects were exposed for more than two years. Samples of blood were collected daily and subjected to haematological analysis. The results obtained showed that in males and females, red blood cell counts (10(6) /mm3) was significantly [P < 0.001] decreased in T1 (4.4 +/- 0.13) and T2 (3.85 +/- 0.07) compared to control (4.76 +/- 0.01). White blood cell counts, haematocrit, haemoglobin concentration and mean corpusclular haemoglobin concentration (MCHC) were significantly [P < 0.01] decreased in both sexes of test groups when compared with control. There was also a significant [P < 0.001] decrease in mean corpuscular haemoglobin (MCH) and mean corpuscular volume (MCV) in test 2 males compared with control. Most subjects exposed for longer than two years (T2) had significantly [P < 0.001] lower values of red blood cell count, haemoglobin concentration and haematocrit than those exposed for less than two years. The odds/odds ratio that a subject would become anaemic progressively rose from less than 1 in the control to greater than 1 or infinity on exposure to petroleum fumes. These results indicate that the petroleum fumes cause a reduction in haematological indices which worsens with prolonged exposure.