In recent years, several rapid diagnostic tests for falciparum malaria have been developed. KAT test results were compared with microscopy on 90 consecutive patients hospitalized at the Hospital for Tropical Diseases, Bangkok, Thailand. Fifty-one patients had P. falciparum infections while 49 had malaria due to other plasmodium species. For a geometric mean +/-SD (Min;Max;range) parasitemia of 11,481 +/- 5.0 (88;713,838;713,750), the sensitivity of the KAT test was 96% (95% CI = 86-99.5), the specificity was 92% (95% CI = 80-99), the accuracy was 94% and the reliability was 85%. These findings suggest that the KAT test is of potential interest in the diagnosis of falciparum malaria in Thailand.