The nucleoside analogue 1-beta-D-arabinofuranosylcytosine (ara-C) is incorporated into herpes simplex virus type 1 (HSV-1) DNA, and this correlates with inhibition of virus replication. The technique of Weigle-type reactivation (WR) was used to compare the ability of induced cellular DNA repair pathways to recognize or repair ara-C incorporated into HSV-1 DNA and ultraviolet (UV)-irradiated virus DNA (254 nm). Pretreatment of monkey cells with low-fluence UV irradiation, growth in cis-dichlorodiammineplatinum(II), or growth in ara-C followed by infection after a 24-hr incubation period resulted in enhanced survival of UV-irradiated HSV-1. Under the same experimental conditions, no reactivation of HSV-1 inactivated by growth in ara-C is observed. Comparisons between uninfected Vero cells exposed to UV irradiation (30 J/m2) or grown in 10(-6) M ara-C demonstrated repair replication in irradiated cells, whereas there was no evidence for DNA repair at various time intervals following removal of the nucleoside analogue. These observations suggest that, once ara-C is incorporated into HSV-1 or eukaryotic DNA, it is not recognized as a repairable lesion within the limits of the DNA repair assays used in these studies.