The diagnostic value of phenotyping acute lymphoblastic leukemia (ALL) of childhood using the immunogold staining method (IGS) was assessed in 34 consecutive new ALL patients seen at Children's Hospital of Pittsburgh during a 14-month period. IGS proved to have considerable value in the diagnosis and classification of ALL. It allowed a sharp and clear identification of surface antigens, documented surface antigen heterogeneity in normal and abnormal cells, and provided a permanent record. The combination with cytochemistries allowed further cytoplasmic identification and correlation. This method does not require sophisticated equipment and can be performed in any laboratory, thus enabling results from different institutions to be more readily compared.