We have obtained a permanent cell line from a squamous cell carcinoma of the vulva. These cells, named CAL39, exhibited morphological, ultrastructural, and immunochemical characteristics of epithelial cells. They were tumorigenic in nude mice. Our observations indicate that the behavior of the cell line in the nude mouse and in culture is similar to that of the original cancer from which it was derived. We have compared these cells with A431 which are currently the best studied model cells of the same tumor origin. Like A431, CAL39 had an elevated number of high affinity EGF receptors, and showed an amplification of DNA sequences at 11q13. We have compared the cytogenetic features of the amplification units in the two cell lines. Unexpectedly, an HSR was present, in both cases, on a marker chromosome which was a derivative of chromosome 11. This result addresses the issue of the in situ amplification of chromosomal DNA.