A parasitological study was performed with 452 malaria patients evacuated from South Vietnam by examinations of their peripheral blood. Results were as follows:

1) The peripheral blood examinations revealed that 52.0% of the examined have parasitemia, of which 95.3% was P. falciparum, one case of P. vivax and the other 10 patients were mixed infected. Neither P. malaria nor P. ovale were found.

2) A total of 1,500 thick and thin blood films was prepared and 707 slides of them (47.1%) showed positive. In P. falciparum, ring forms were found most frequently and the next was gametocytes. Eighty slides (50%) showed mixed together with both ring form and gametocytes. All of the erythrocytic stages were seen in three slides of P. vivax.

3) Weekly periodical examinations showed 233.8 parasite density every 1,000 W.B.C count in average, while occasional at fever attacks 531.7.

4) Size of gametocytes in P. falciparum was 9.31(±0.89) by 2.16(±0.53) in macrogametocyte and 6.61(±0.82) by 2.51(±0.35) in microgametocyte. Their sex ratio was 100 : 92.

5) Repeated blood examinations showed increased detection rates. The positive rate of parasitemia was 52.0% in single examination, increasing in succession with repetitions.