Oxidative stress is a metabolic situation used by immune cells to provide protection against infection. Under activation by threatening elements, phagocytes produce chemically toxic molecules, namely the reactive oxygen species (ROS) and reactive nitrogen species (RNS). This mechanism involves two types of enzymes: NAPDH oxidases (NOX) and NO synthases (NOS), which activities are versatile and not fully understood yet. In this regard, we studied in real-time the release of bursts of ROS and RNS by single PLB-985 cells, originating from a myeloid cell line prone to differentiate into neutrophil or monocyte-like phagocytes. A selective electrochemical detection of each ROS or RNS was conducted at platinized carbon fiber microelectrodes positioned at micrometric distances from single cells. Our results show (1) the existence of a NO synthase activity in PLB-985 cells and (2) the ability of NO synthases to provide a NOX activity in cells where NADPH oxidase (NOX2) is knocked out.