Supercoiled infectious DNA was isolated from nuclear polyhedrosis virus infecting great wax moth Galleria mellonella L.) Covalently closed DNA molecules constitute approximately 10--30 per cent in our preparations. These molecules dissappear during storage. Electron micrographs of supercoiled and open circular molecules are presented. Length of the open rings is about 50--52 micron. Infectivity of different DNA forms is discussed.