Addition of p-aminobenzoic acid, inositol, thiamine, nicotinic acid, or choline chloride did not provide significant UV protection for gypsy moth,Lymantria dispar(L.), nucleopolyhedrosis virus (NPV), while the addition of pantothenic acid, pyridoxine, folic acid, and riboflavin protected NPV. Pantothenic acid and pyridoxine (at 1%) increased UV protection significantly by factors of 1.88 and 2.08, respectively, which resulted in 52–57% of original activity remaining. Folic acid (93% original virus activity remaining [OAR]) and riboflavin (94% OAR) were superior protectants, and enhanced UV tolerance by 3.3- and 3.4-fold, respectively. Riboflavin provided little protection at 0.10%, some protection at 0.25%, and significant protection at 0.50 and 1.00%. The effect was concentration-dependent, and 1.00% riboflavin preserved 80% of original viral activity. Even at 0.10% concentration, folic acid enhanced UV persistence, and 87% of original activity remained with addition of 1.00% folic acid. Folic acid is a substituted pteridine, with both p-aminobenzoic acid and glutamic acid in the side chain. A pterin, xanthopterin, was almost as effective as folic acid, and 89% of the folic acid activity could be accounted for by the pterin alone. However, both p-aminobenzoic acid and glutamic acid (at 1.00%) were ineffective, either alone or in combination.