The cytotoxicity of the iridium complexes 3 and 4 has been investigated on human melanoma A-375 cells and non-cancer HFF-1 cells (human foreskin fibroblasts) by MTT cell viability assays. The results obtained after 24h, 48h and 72h of incubation are summarized in Table . ). However, for complex 3, similar cytotoxic properties was determined on both cell lines (Table ). Increased toxicity towards cancer cells over healthy cells is highly desirable for compounds for therapeutic or diagnostic applications.