Abstract: Methods for the treatment and prevention of human, animal and plant viral infections are provided. The methods consist of administering to an infected human, animal or plant an effective amount of DNase and RNase or other nuclease exhibiting properties of both enzymes, preferably in conjunction with a suitable divalent cation activator. The effective amount preferably provides a systemic or local concentration between about 5.times.10.sup.-3 to 10.times.10.sup.-3 Kunitz units of activity of each nuclease per ml of body fluids and between about 0.1 to 0.3 Kunitz units or more per ml of solution for incubating, growing, soaking or spraying plant seeds, microclones, seedlings or adult plants.