The onset of oxidative stress occurs as a result of an imbalance between free radical scavenging capacity of antioxidants and reactive oxygen species (ROSs). This leads to the induction and progression of many disorders including cancer. The overall aim of this study was to establish the interaction between oxidative stress and carcinogenesis. Venous blood samples of cancer patients (n=30) receiving chemotherapy regimen in Lagos University Teaching Hospital, Lagos, Nigeria and human volunteers (n=50) with no previous history of cancer were collected. Plasma levels of nitric oxide (NO), total glutathione (TGSH), cortisol and some haematological parameters were determined spectrophotometrically. Results showed that there were significant (plt;0.05) differences in the levels of plasma NO, TGSH and cortisol in cancer patients compared to the control. The levels of NO, TGSH and cortisol were observed to be independent of the histopathological grade of cancer and non‐parametric clinical data such as age and sex. NO positively and significantly (plt;0.001) correlated with TGSH (r=0.588). Haematological analysis showed that the levels of White Blood Cells (WBC), Red Blood Cells (RBC), Hemoglobin (HGB) and Packed Cell Volume (PCV) were significantly (plt;0.05) lower in cancer patients compared to the control. Present investigation has shown that NO, TGSH and cortisol can indicate oxidative stress and therefore they can be used as biomarkers in cancer diagnosis. Likewise, results also indicated that changes in haematological parameters may be eminent in cancer patients.