Background : Studies have shown that Na⁺-K⁺ ATPase activity was altered in disrupted red blood cell membranes and this enzyme is believed to be the site of active transport of Na⁺ and K⁺ in intact red blood cells. The enzyme is often referred to as Na⁺- K⁺ pump because it pumps Na⁺ out and K⁺ into the cell against gradients with the concomitant hydrolysis of intracellular ATP. Objective: The aim of this study was to find out the possibility of using Na⁺-K⁺-ATPase activity as a biomarker for the diagnosis of individuals with different physiological conditions. Materials and methods: The activity of Na⁺-K⁺ ATPase was determined in blood samples collected from different pathological and physiological conditions such as pregnancy, smoking, diabetes and renal dysfunction compared with healthy subjects matched for age and sex. Results: The Na⁺-K⁺ ATPase activity in pregnancy (0.094 ± 0.0051 μM Pi/min. mg protein), smoking (0.064 ± 0.0011 μM), diabetes (0.047 μM 0.002 μM) and kidney disease (0.069 ± 0.0014 μM) was higher compared to the measurements in healthy individuals (0.0081 ± 0.0031 μM). Conclusion : Na⁺- K⁺ATPase specific activity is a biomarker for the diagnosis of individuals with different physiological diseases.