We have performed an in vitro study of the growth-inhibitory capacity of the potent and long-acting NK1 receptor antagonist L-733,060, at concentrations ranging from 2.5 microM to 20 microM, against the neuroblastoma cell line SKN-BE(2) and 10 microM to 25 microM for glioma cell line GAMG. Coulter counter was used to determine viable cell numbers, followed by application of the tetrazolium compound [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)2-(4-sulfophenyl)-2H-tetrazolium], inner salt colorimetric method to evaluate cell viability in this cytotoxicity assay. L-733,060 inhibited the growth of the two cell lines studied in a dose-dependent manner. The IC 50 values were 11.6 microM (30h) and 10.2 microM (72h) for SKN-BE(2); and 21.3 microM (48h) and 19.9 microM (96h) for GAMG. These findings indicate that the NK1 receptor antagonist L-733,060 acts as a broad-spectrum antitumoural agent. This new action, reported here for the first time, suggests that the NK1 receptor antagonist L-733,060 could be a promising therapeutic drug for the treatment of human neuroblastoma and human glioma.