Germicidal UV (also known as UVC) provides a means to decontaminate infected environments as well as a measure of viral sensitivity to sunlight. The present study determined UVC inactivation slopes (and derived D 37 values) of viruses dried onto nonporous (glass) surfaces. The data obtained indicate that the UV resistance of Lassa virus is higher than that of Ebola virus. The UV sensitivity of vaccinia virus (a surrogate for variola virus) appeared intermediate between that of the two virulent viruses studied. In addition, the three viruses dried on surfaces showed a relatively small but significant population of virions (from 3 to 10 % of virus in the inoculum) that appeared substantially more protected by their environment from the effect of UV than the majority of virions tested. The findings reported in this study should assist in estimating the threat posed by the persistence of virus in environments contaminated during epidemics or after an accidental or intentional release.