A high incidence (37 out of 188) of anti-IA cold agglutinins was found in the sera of indigenous New Guineans living at Minj (alt. 1,600—1,800 m) in the Western Highlands District of New Guinea. Anti-IA did not occur in three other populations tested, although these possessed a high incidence of anti-I antibodies. The earlier findings concerning the incidence of specificity of cold haemagglutinins in New Guinea are reviewed and it is suggested that they may be induced by different agents, probably of a parasitic nature, in different localities. It is predicted that cold agglutinins should be found in other populations which are subject to high rates of infection similar to those in New Guinea.