General Summary In Part I of this study six therapeutic regimens employing four different 8-aminoquinoline derivatives were tested under strictly controlled conditions in mosquito-transmitted Chesson strain vivax malaria, experimentally induced in volunteers in a Federal penal institution. Thirty-four men were treated with each regimen. Test drugs were given every 6 hours for 14 days, in combination with quinine sulfate, 250 mg. of base every 6 hours for the same period. The relapse incidence after primary attacks was as follows: Primaquine 20 mg. (base) daily 15 per cent Primaquine 10 mg. (base) daily 65 per cent Isopentaquine 60 mg. (base) daily 35 per cent SN-3883 60 mg. (base) daily 9 per cent SN-3883 30 mg. (base) daily 21 per cent Pamaquine 60 mg. (base) daily 82 per cent Although toxic manifestations were not alarming with any of the compounds, primaquine at the effective dosage of 20 mg. per day was exceptionally well tolerated, and under the conditions of the test was regarded as the best of the four drugs. Part II of the study dealt with the trial of three therapeutic regimens employing two different 8-aminoquinolines under the same conditions as outlined above. Ten men were treated with each regimen. The test drugs were given in a single dose daily for 7 days; chloroquine, 1.5 gm. (base) total dose, was given concomitantly during the first 3 days for the management of the acute attack. Relapse incidence after the acute attack was as follows: Primaquine 30 mg. (base) single dose daily 90 per cent Primaquine 20 mg. (base) single dose daily 80 per cent SN-3883 60 mg. (base) single dose daily 100 per cent There were no toxic manifestations, but the high relapse incidence indicates the limited curative efficacy of these shorter regimens against severe Chesson strain vivax infections and consequently that they are not generally applicable curative regimens.