A protocol was developed to measure granulocyte activity. The protocol methodology measured the hydrogen peroxide released after granulocytes activation by PMA (phorbol 12-myristate 13-acetate) by using the Amplex Red assay, which included count cells by flow cytometer and measurement kinetic curve of NADPH oxidase activity by fluorometer. Two parameters were used to describe the level of granulocyte activity: (1) the initial rate of NADPH-oxidase enzyme and (2) level of hydrogen peroxide released after 20 min of granulocyte activation. The method was applied to measure granulocyte activity in healthy and ill subjects and demonstrated that applied procedure is sensitive for estimation of the disease activity. There was a decrease in granulocyte activity in patients with cancer or diabetes mellitus, and an increase in activity in patients with osteo and rheumatoid arthritis or with viral and fungal infection.