BA-41,799, a tetrahydrofuran derivative that at one time attracted considerable interest as an antimalarial agent because of a combination of structural novelty with activities against infections with Plasmodium berghei and Plasmodium berghei yoelii in mice, has been evaluated for its capacities to effect prophylaxis and radical cure in rhesus monkeys challenged or already infected with sporozoites of the drug-susceptible Ro strain or the pyrimethamine-resistant Ro/PM strain of Plasmodium cynomolgi, and for its capacity to effect suppressive cure of infections with trophozoites of these strains. At doses up to the maximum tolerated, BA-41,799 had only marginal activity against infections with the Ro strain and none against the Ro/PM strain. On the basis of past experiences, the above results suggest that BA-41,799 would have little to offer for prophylaxis, radical cure, or suppression of human infections with Plasmodium vivax.