BACKGROUND: In South Korea, indigenous malaria has been reappeared since 1993 and more than 350 cases diagnosed in 1996. For the diagnosis of malaria the classic methods such as thin and thick blood smears with Giemsa or Wright stain has been routinely used. Since recently fluorochrome staining has been shown to be more sensitive, easy to do, and less time-consuming, we applied the new method, Acridine orange stain, for diagnosis of clinically suspected cases. METHODS: Thin and thick blood smears were prepared from civilian patients of Kyunggi Province (n=20) and Republic Of Korea army patients pre- (n=67) and post-treatment (n=13) of malaria. The slides were fixed by methanol and stained by either Giemsa or Acridine orange solution (10-50 g/mL). For comparison, an expert on malaria diagnosis examined them by light and fluorescent microscope, respectively. RESULT: Acridine orange stain was found to be a rapid technique, and as sensitive (83%) as thick smears (83%) for diagnosis of malaria. The detection limit of acridine orange stain was 23.5 parasites/ul of blood. The staining time was much shorter (30 sec) than that of Giemsa stain (30-60min). CONCLUSION: Acridine orange stain is evaluated as a simple, rapid, and sensitive method for malaria diagnosis compared with Giemsa stain.