aThe toxicity of ferrocenylethyl benzotriazole (1) and other ferrocene compounds including ferrocenylmethyl benzimidazoles (4,5,6,11), ferricenium salts (3,9,10) and ferrocenylmethyl adenine (7), was studied. All ferrocene complexes under investigation showed low or medium toxicities. On the basis of an earlier model of chemical carcinogenesis, the antitumor activity of ferrocenylalkyl azoles 1, 8 and ferricenium salts 9, 10 was studied in vivo in the so-called sub-capsular test on human tumors. This effectiveness was compared with that of cisplatin. A series of ferrocenylalkyl azoles were synthesized by interacting azoles either with α-hydroxyalkyl ferrocenes FcC(OH)R 1 R 2 in organic solvent in the presence of aqueous HBF 4 in quantitative yields or with trimethyl(aminomethyl)ferrocene iodide in an aqueous-basic medium in good yields. The X-ray determinations of molecular and crystal structures of α-(1-benzotriazolyl)ethylferrocene (1) and α-(1-naphthatriazolyl)ethylferrocene (12) were performed.