Blood samples collected from five volunteers participating in a P. falciparum infectivity trial were examined to determine the efficacy of the acridine orange technique. Several lens configurations were tested for efficiency in the diagnosis of malaria using this system. There was no significant difference in the sensitivity for detecting positive specimens or number of parasites among three lens configurations: a 50 × long working distance objective (0.34mm) with either a 10 × ocular (total magnification 500 ×) or a 12.5 × ocular (625 ×) and a 750 × configuration using a 50 × objective with a shorter working distance (0.24mm). All three lens configurations were significantly better than the 1,000 × configuration using a commonly available 100 × oil immersion objective. The results achieved using this lens still exceeded the sensitivity of the thick blood film.