Titanium dioxide (TiO2) reflects ultraviolet light, and so could be expected to protect the occlusion bodies (OBs) of nucleopolyhedroviruses (NPVs) from degradation by sunlight. However, in the presence of sunlight and water, TiO2 catalyzes the formation of hydrogen peroxide, which can degrade OBs. We tested microfine TiO2 that had been photostabilized (particles were coated to prevent catalytic activity), as a UV protectant for the OBs of the NPV of Helicoverpa zea (Boddie). In the absence of UV, activity of the OBs was reduced by nonphotostabilized TiO2 but was unaffected by photostabilized TiO2 or by zinc oxide (ZnO). None of these materials influenced larval feeding rates. Under simulated sunlight, photostabilized TiO2 protected the OBs to a greater degree than did ZnO. Photostabilized TiO2 was compatible with a viral enhancer, the fluorescent brightener Blankophor HRS. Under simulated sunlight, both materials increased activity of the OBs, relative to OBs with neither material, in a largely additive manner. In bioassays of foliage collected from field plots of lima bean plants sprayed with OBs with or without one or both of these materials, TiO2 increased persistence of the OBs, but Blankophor HRS had no significant effect.