Eight squamous cell carcinomas from the head and neck region were established as xenograft lines in nude mice and tested for their sensitivity to the antineoplastic drugs bleomycin and cisplatin. Tumor volume, histology, DNA flow cytometry and mitotic activity were used as parameters. One out of the 8 tumours appeared to be highly sensitive to bleomycin, while three other tumours were sensitive to both bleomycin and cisplatin. These observations are in good correlation with the reported data in patients. All chemosensitive tumours showed regrowth after the cytotoxic drug treatment had been completed. No change was seen in the chemosensitivity of other features of the regrown tumours, not even after repeated exposure to the drugs. Comparison of the tumour volume with the other parameters applied indicated that the tumour volume of squamous cell carcinomas was not always a reliable parameter for testing chemosensitivity, because of the important contribution of keratin to the tumour volume. It is concluded that additional parameters such as histological examination, DNA flow cytometry or mitotic activity are necessary in order to draw reliable conclusion on xenografts with a large avital component. In addition, DNA flow cytometry has proved to be very useful for the rapid screening of drug sensitivity.