Host cell reactivation (HCR) of viruses has been used in the past to assess the DNA repair capacities of various mammalian cell types. In this study, a PCR-based HCR technique was developed for determining DNA repair capacity of mammalian cells. Many DNA lesions, including UV photoproducts, block DNA amplification by Taq polymerase, and the exponential nature of PCR imparts a tremendous potential for quantifying the remaining non-adducted DNA templates from small samples. Ad5HCMVspl ZacZ is a recombinant nonreplicating adenovirus (Ad) containing the lacZ reporter gene under the control of the human cytomegalovirus (HCMV) immediate early promoter inserted into the deleted El region of the viral genome. This virus is unable to replicate, but it can efficiently express the reporter gene in many types of mammalian cells, including human fibroblasts. Using quantitative PCR, the induction and repair of UV photoproducts was measured in a 2.6 kb region of the lacZ reporter gene inserted into the deleted El region of Ad5HCMVspllacZ and in a 2.8 kb region of the endogenous E4 region of the virus. Primers flanking the regions were added to equal amounts of DNA extracted from cells infected with unirradiated or UV-irradiated Ad5HCMVspl lacZ and each sample was amplified by PCR using radiolabelled nucleotides as substrates. PCR products were separated by agarose gel electrophoresis and quantified using a phosphorimaging system. Results show a simple exponential decrease in PCR product with increasing UV fluence to the virus. There was a significant removal of UV photoproducts by 24 hours after infection of normal human fibroblasts. A reduced capacity for lesion removal was detected after infection of nucleotide excision repair deficient fibroblasts derived from patients with xeroderma pigmentosum (XP) and Cockayne syndrome (CS). Previous work from our lab using a P-gal reporter gene assay has shown that both UV light and heat shock treatment of cells prior to infection with UV-damaged Ad5HCMVspl lacZ enhances HCR. Application of the quantitative PCR technique to the study of inducible repair shows there is an enhancement in the rate of lesion removal from both regions of the vector in UV-irradiated normal lung fibroblast cells, compared to unirradiated cells. This demonstrates that previous reports of enhanced host cell reactivation are indicative of a genuine enhancement of DNA repair. Also, the P-gal reporter gene assay was used to investigate inducibility of UV lesion repair by ionising radiation; no significant increase in HCR of p-gal activity was found in cells treated with y-rays compared to untreated cells. / Thesis / Master of Science (MS)