A procedure for the determination of the gamma chain heterogeneity of adult human blood samples with low Hb F has been developed. It consists of the isoelectrofocusing of lysates at a rather high hemoglobin concentration, the isolation of the focused Hb F by elution from the gel, and the analysis of the isolated hemoglobin by reversed phase high performance liquid chromatography for the separation and quantitation of globin chains. Depending on the isoelectrofocusing apparatus, many samples with as little as 1% Hb F may be focused in a single run and the gamma chain composition of the recovered hemoglobin (enriched from 15% to 95% in Hb F) easily analyzed by high performance liquid chromatography. The same procedure might be used for the isolation of low level hemoglobin variants for structural studies.