In this study we examined the effects of rHRG on tyrosine phosphorylation of the ErbB2, ErbB3, and ErbB4 proteins in nuclear fractions of colon cancer cell lines.After immunoprecipitation with an antibody against phosphotyrosine (PY-20), western blot analyses revealed that both the DLD-1 and Caco-2 cell lines express a protein with a molecular weight of approximately 180 kD reacting against antibodies to the ErbB2 (C-18) and ErbB3 (C-17) proteins (Figure 1A). The gene discussed is ERBB4; the disease is malignant colon neoplasm.