The discovery of antimalarial properties of derivatives of 8-aminoquinolines which combine high activity against the tissue stages of the malaria parasite with satisfactory tolerance by man can be said to have marked the final stage in the search for a radical cure of vivax malaria. Since its synthesis in the USSR in 1952, quinocide-an 8-aminoquinoline drug-has been subjected by Soviet workers to intensive research, an outline of which is presented in this paper. The results of their investigations, which ranged from laboratory and clinical studies of tolerance to the drug, through small-scale trials of its parasiticidal activity, to large-scale studies on the effectiveness of its mass administration are very encouraging. Both for anti-relapse treatment and for pre-epidemic prophylaxis, a short (10- or 14-day) course of quinocide proved as effective as a lengthy course of acriquine with plasmocide. Side-effects were infrequent, and most of those that occurred were transient and did not necessitate the suspension of treatment. It is suggested that the mass administration of quinocide would, in certain cases, be a useful adjunct to insecticidal measures in the clearance of malaria foci.