Fluorescent rhodacyanines, which display antimalarial activity in vitro and in vivo, stain plasmodial parasites at the erythrocytic stage. A good correlation between the antimalarial activity and the accumulation of the dyes is observed. A fused-rhodacyanine, which displays a strong fluorescent property itself, was designed as a new probe for plasmodial parasites. It appears to be specifically localized in the parasitic mitochondria.