Xeroderma pigmentosum complementation group A (XPA) is one of the DNA repair deficient syndromes. The cell biological features of XPA were examined by flowcytometry using Epstein Barr (EB) virus-transformed lymphoblastoid cells. Cellular sensitivity to vincristine (VCR), etoposide (VP-16) and methotrexate (MTX) were assayed by DNA pattern changes by flowcytometry. Recently, ataxia-telangiectasia (AT), one of the same kind of disorder, has been reported to have an increased sensitivity to VCR and VP-16. However, AT showed some resistance to MTX according to other reports. Our results showed that XPA had an increased sensitivity to VCR and also to VP-16. Moreover, different from AT, XPA showed some sensitivity to MTX. Thus there is some cell biological similarity between XPA and AT, as well as some difference of the abnormality in the DNA repair pathway.