The AnaeroPack^® malaria culture system with a portable thermostat incubator was evaluated in a field laboratory on the Thai-Myanmar border conducting in vitro drug susceptibility tests on blood samples from 5 Karen children infected with P. falciparum. Only one isolate was susceptible to chloroquine; the others were highly resistant. The IC₅₀ value of an isolate was only resistant to mefloquine, whereas the values of the 3 patients who presumably showed recrudescence were slightly elevated in the susceptible ranges. These results suggested that chloroquine should no longer be used for P. falciparum malaria in this geographic area, and that mefloquine should be carefully monitored for its in vivo effectiveness. In this study, the AnaeroPack^® malaria culture system with portable thermostatic incubator is a powerful and useful mobile tool, which aids in providing detailed evidence-based distribution data concerning of drug resistant malaria in the field.