Infectious pancreatic necrosis (IPN) virus has been purified and some physicochemical properties of its nucleic acid and protein moieties have been determined. The buoyant density of the virus particle in CsC1 is 1.35 g/ml; degraded particle banded at a density of 1.31 g/ml. The virus nucleic acid was found to be doublestranded, according to several different criteria, namely resistance to pancreatic RNase, low density in Cs2SO4 (I'615), sharp melting curve with a T~ of 89 °C in hypotonic

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... , and base composition. In a sucrose gradient the bulk of the virus RNA banded as a single peak (i 4 S); a small part of the virus nucleic acid was found at the top of the gradient. By gel electrophoresis virus RNA was resolved into three peaks corresponding to double-stranded molecules with mol. wt. ranging from 2"8 5 × I06 to 2"55 × I06. Gel analysis of virus proteins revealed three polypeptides of tool. wt. 8o, 5o and 3o × IO ~, representing respectively 3 ~, 68 9/00 and 29 ~oo of the total protein. On the basis of these results IPN virus appears to be related to some reo-like viruses, having a single protein shell and a single class of double-stranded RNA.