We have recently examined a number of potential riboflavin antagonists for antimalarial activity. l Several 5-deazaflavins, including 5-deazariboflavin, were found to be inactive in vivo, while l0-(4-chlorophenyl)-3-methyl-flavin (1) was very active against Plasmodium vinckei in mice by both oral and intraperitoneal (ip) administration and against Plasmodium falciparum in culture. Our rationale for testing such compounds was based on the ...