3-Hydroxy-N'-arylidenepropanehydrazonamides represent a new class of antiplasmodial compounds. The two most active phenanthrene-based derivatives showed potent in vitro antiplasmodial activity against the 3D7 (sensitive) and Dd2 (multidrug-resistant) strains of Plasmodium falciparum with nanomolar IC50 values in the range of 8-28 nM. Further studies revealed that the most promising derivative, bearing a 4-fluorobenzylidene moiety, demonstrated in vivo antiplasmodial activity after oral administration in a P. berghei malaria model, although no complete parasite elimination was achieved with a four-dose regimen. The in vivo efficacy correlated well with the plasma concentration levels, and no acute toxicity symptoms (e.g., death or changes in general behavior or physiological activities) were observed, which is in agreement with a >1000-fold lower activity against L6 cells, a primary cell line derived from mammalian (rat) skeletal myoblasts. This indicates that lead compound 29 displays selective activity against P. falciparum. Moreover, both phenanthrene-based derivatives were active against stage IV/V gametocytes of P. falciparum in vitro.