For chemosensitivity testing, a rapid in vitro colorimetric method (MTT assay) was used. Eleven head and neck cancer cell lines were investigated to distinguish five known active agents from five compounds inactive in phase II studies. Evaluation of the reliability of the assay for assessing drug sensitivity in this tumor cell population was done by correlating the in vitro results with reported in vivo response data. Methotrexate and cisplatin (clinically active) and vindesine and doxorubicin (less active clinically) were recognized in vitro as active and correlated well with clinical experience. Bleomycin (clinically active) was ineffective against some cell lines. The in vitro findings for the clinically inactive drugs (deoxyazacytidine, lomustine, and carmustine) also corresponded. Amsacrine and etoposide, contrary to clinical experience, showed activity in vitro. Further comparison of MTT assay results with clinical data is warranted and essential before its use in large-scale drug screening studies.