The circular DNA molecules of cotton bollworm nuclear polyhedrosis virus, visualized by electron microscopy, have a mol. wt. of 81 x 106. In addition, renaturation kinetics studies suggest a genetic complexity corresponding to a mol. wt. of 82 x 106. A G+C content of 42% for the virus DNA is estimated from its thermal denaturation profile and buoyant density in CsCl.