Rhabdomyosarcoma (RMS) cells were incubated with four vanadium compounds: cations BMOV and vanadyl sulphate, and anions ortho- and metavanadate. Growth inhibition of RMS cells in the culture was determined by two staining methods: with N-hexamethylpararosaniline (crystal violet = CV) or bromide 3-(4,5-dimethylthiazol-2)-2,5-diphenyltetrazolium (MTT). After 48 h incubation with 10-40 μM for NaVO3 or 20-40 μM for the other three vanadium salts, the results were statistically significantly lower (0.001 < p < 0.01) as compared to the controls (without vanadium in the medium). A vanadium concentration higher than 40 μM resulted in cell destruction or death in all cells. A comparison with our previously obtained results showed the greatest sensitivity of rat hepatoma H 35-19 cells in comparison to four human cancer cell lines (A549, DU145, HTB, RMS). Investigations of human cancer cells demonstrated that the highest resistance to orthovanadate was characteristic of RMS (c.40 μM) and HTB (c. 20 μM). Electron microscopic examination showed pleomorphic nuclei with visible amounts of heterochromatin and large nucleoli, characteristic of RMS cells. Cells at various stages of differentiation were observed.