Slides prestained with acridine orange (AOS) were used for direct examination of microorganisms in clinical specimens. The method is simpler than a commonly used acridine orange stain (AO) and has the advantage of being a supravital stain. Results indicate that the AOS method is sensitive, and allows rapid detection of microorganisms, even in the specimens containing few microorganisms, e.g. cerebrospinal fluid. Moreover AOS may be the choice method for detection of Trichomonas vaginalis.