Seven different ferrocene derivatives have been tested in vitro against Ehrlich ascites tumor cells. Neither ferrocene nor the monosubstituted derivative N, N-dimethylaminomethylferrocene showed cytotoxic activity (IC50 > 1000 mu M for 3 h treatments). Better results were obtained with 1,2-disubstituted derivatives. The IC50 values ranged from 376.6 mu M for 1,2-diformylferrocene to 71.2 mu M for racemic 2-( N, N-dimethylaminomethyl) ferrocenecarboxamide. The latter derivative was also encapsulated in native beta-cyclodextrin ( CD), heptakis-2,3, 6-tri-O-methyl-beta-CD (TRIMEB) and 2-hydroxypropyl-beta-CD (HP beta CD) to give 1: 1 (host: guest) inclusion compounds. The existence of true inclusion complexes in the solid state was confirmed by a combination of powder X-ray diffraction, thermogravimetric analysis, FTIR and C-13 CP MAS NMR spectroscopy. The IC50 value for the beta-CD inclusion compound was identical to that obtained for the nonincluded ferrocene derivative. By contrast, the inclusion compo