We developed a simple technique for the isolation of NADPH oxidase (Nox) in a soluble form from the brain-cell membrane (BCM) of rats based on the ability of Nox to form an unstable complex with ferrihemoglobin (ferriHb). It was shown for the first time that ferriHb (2 × 10−6 M) stimulates Nox release from the BCM to the soluble phase after a 2 h aerobic incubation of an aqueous mixture of these membranes at 37°C and pH 8.0 ex vivo. The optical and acid-base characteristics of Nox, as well as the NADPH-dependent O 2 − -producing and ferriHb-regenerating activities of the enzyme from the BCM, are similar to the properties of Nox from membranes of other cell types (spleen, erythrocytes, and bone marrow). A synthetic analogue of the neuroactive proline-rich polypeptide (PRP-1) of the neurosecretory granules of the hypothalamus, so-called galarmin (to 10 mg), suppressed ferriHb-induced release of Nox and stimulated the O 2 − -producing and ferriHb-regenerating activities of the enzyme in a concentration-dependent manner. We conclude that the release of soluble Nox from the BCM occurs due to membrane destabilization in the presence of ferriHb and that the suppression of Nox release by galarmin may be caused by its membrane-stabilizing effect. The results also suggest that galarmin is involved in the regulation of oxygen homeostasis in brain tissue.