Isolation and purification of L-lysine-2- monooxygenase from the bacterium Pseudomonas species was carried out. The purification procedure included ammonium sulfate fractionation, acid treatment, gel filtration through Sephadex G-200 and ion-exchange chromatography on DEAE-Sephadex A-50. Such treatment resulted in more than 220-fold purification and 22% yield; the specific activity of the enzyme is 14.6 U/mg. The enzyme spectrum is typical for flavoproteins, with peaks at 275, 386 and 462 nm. At 460 nm excitation, the enzyme fluorescence has an emission maximum at 530 nm, whereas at 360 nm extication--at about 520 nm. The molecular mass of L-lysine-2-monooxygenase as determined by SDS/PAAG electrophoresis is about 268 kD. The KM values for oxygen and lysine are equal to 6.5.10(-4) M and 2.3.10(-4) M, respectively. The curve for the dependence of the reaction rate on lysine concentration is sigmoidal. It was assumed that the electrophoretic behaviour of the enzyme confirms the hypothesis on the nature of allosteric regulation of the enzyme activity by alterations in the regulatory site charge.