We compared the effectiveness of malaria diagnosis by means of direct observation of centrifuged blood with that by conventional examination of Giemsa stained blood-films in a malaria clinic in Ethiopia. A commercially available, modified hematological apparatus (the QBC tube) was used for centrifugation. Red blood cells infected with diverse stages of Plasmodium falciparum and P. vivax are lighter than noninfected cells and somewhat heavier than granulocytes; thus they can readily be detected by direct inspection of UV-illuminated tubes. About 10% of infections diagnosed by direct centrifugal microscopy in a clinical setting were not detected by conventional examination of stained thick films. Diagnosis by direct centrifugation appears to be at least 8 times as sensitive as conventional microscopy when applied to serially diluted samples of malaria-infected blood. Superior sensitivity, together with the one step, solid state nature of the direct centrifugal procedure, provides important advantages for malaria diagnosis.