The ferrocenyl diphenol 1 [1,1-bis(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene] displays strong cytotoxic effects against a variety of cancer cells. In the present study we have evaluated the immunomodulatory and antiparasitic activities of compound 1 and its protected dipalmitate analogue 2. We have furthermore compared the antiparasitic results of 1 and 2 with the organic analogue, 3 [1,1-bis(4-hydroxyphenyl)-2-phenyl-but-1-ene], where the ferrocenyl group has been replaced by a phenyl ring. When assayed against normal (noncancerous) splenocytes, all compounds were considered nontoxic. Compound 1 inhibited NO production by macrophages, inhibited concanavalin A-induced lymphoproliferation, and was active against Leishmania amazonensis and Trypanosoma cruzi. Compound 2 had lower activity in all assays performed. Surprisingly, compounds 1 and 2 exhibited similar and significant activity against Plasmodium falciparum, with IC(50) values of 3.50 and 1.33 mu M, respectively. Compound 3 showed an inverse activity profile, being active against T. cruzi but far less active against P. falciparum. Drug Dev Res 71:69-75, 2010. (C) 2009 Wiley-Liss, Inc.