A strain of Plasmodium falciparum isolated in the Republic of Panama in March 1972 was transferred to the Unit on Human Malaria (LPD, NIAID, NIH) in Atlanta, Georgia. Studies in eight non-immune prisoner volunteers demonstrated that infections with this Panama II strain of P. falciparum recrudesced following treatment with chloroquine 1.5 g (base), amodiaquine 1.4 g (base), chlorguanide 1.3 g (base) over 5 days, or quinine 11.34 g (base) over 7 days. Parasitemia increased during therapy with pyrimethamine 150 mg over 3 days. Infections were cured by treatment with quinine for 10 days (16.2 g base) or by combination therapy with sulfadiazine (10 g in 5 days) plus pyrimethamine (150 mg in 3 days).