The three organometallic complexes [(Cis-PtII (DDH) (2,5-Dihidroxibenzensulfonic)2, RhI (CO)2 Cl(2-Aminobenzothiazole) and RhI (CO)2 Cl(5-Cl-2-Methilbenzothiazole)] used in this study had been previously found to have a high in vitro activity against promastigote and amastigote like forms of Leishmania donovani. Here, the cytotoxic effect of these new organometallic complexes on the J-774 macrophages were studied. Only the RhI(CO)2 Cl (2-Aminobenzothiazole) complex induced substantial toxicity in the cells. Also, we assayed the effect of this complex on the parasite's biosynthesis of macromolecules. The RhI(CO)2Cl (5-Cl-2-Methylbenzothiazole) complex inhibited DNA, RNA, and protein synthesis. On the other hand, the two other compounds tested did not inhibit the incorporation of radioactive precursors. Finally important ultrastructural alterations in the parasites treated with the two non-cytotoxic complexes were observed.