Detailed hematological investigations have been performed on 78 apparently healthy male and nonpregnant female adult inhabitants of Kar Kar Island, off the coast of mainland New Guinea. Only one subject had a normal hemoglobin level. Iron deficiency was the major factor contributing to the almost universal anemia. In men it appeared due to a combination of inadequate intake and some increase in gastrointestinal losses, but in women failure of utilization of iron also played a part. Overt folate deficiency was uncommon, but marginal folate deficiency occurred in 15% of subjects studied. Vitamin B12deficiency did not occur. The presence of heterozygous β-thalassemia neither protected against iron deficiency nor contributed significantly to the general level of anemia. The overall contribution of malaria to anemia could not be directly assessed, although the low density of parasitemias and the lack of association with folate deficiency or gross splenomegaly indicate a relatively minor ce:role.