Abstract: 52 patients of acute falciparum malaria were tested with the WHO Extended Field Test at Kusei County and Huaibin County of Henan Province respectively in 1982 and 1983 for sensitivity of P. falciparum to chloroquine. The results showed that the patients' temperature became normal within 46.4 hours in average and asexual blood parasites were completely eliminated within 59.0 hours after the treatment. Only 2 patients' blood parasites were completely eliminated by the sixth day and the seventh day, respectively. Of 52 cases tested in vivo, 9 were tested by the in vitro test simultaneously. The results suggested that 3 cases showed inhibition of parasite growth at 8 pmol, of whom, asexual blood parasites were completely eliminated by the sixth day by the in vivo test in one case.The results obtained showed that the P. falciparum in South Henan appeared to have an incipient chloroquine resistance.