We searched for Human Epidermal growth factor Receptor (HER)-related transcripts using 14 human leukemia/lymphoma cell lines, assuming that cell lines grown in vitro are representative of malignant leukocyte lineages and stages of development. A unique truncated HER1 transcript was observed in 3 out of 4 Burkitt B lymphomas and 1 Erythroblastoid leukemia (K562), which was absent in healthy peripheral blood mononuclear cells and in pre-B leukemia cell lines. In agreement with the reported down-regulation of HER1 in normal leukocyte development, this finding suggests a resumption of HER1 expression during B cell malignant lymphoma development as a secondary and relatively late event, posterior to IgH rearrangement. Healthy mononuclear cells down-regulated HER1, but were positive for its ligands and for HER2, suggesting underestimation of the presence of “HER system” in mature peripheral blood cells.