Phosphlipase C(PLC) is one of the key molecules in signal transduction for cellular activity such as proliferation and differentiation. Phospholipase C-γ1(PLC-γ1), which is an isoenzyme of PLC and has homology of src oncogene, is a biologically important enzyme in cell proliferation. However, the biological significance of their molecules in carcinogenesis or tumor progression is not defined yet. Recently it has been reported PLC-γ1 might involve in activation of ras gene, whose mutation is found in most lung cancer tissue. Therefore we have performed immunohistochemical staining for PLC-γ1 and ras-oncoprotein on 15 cases of laryngeal squamous cell carcinoma and 8 cases of squamous papilloma as control group to clarify the relationship of PLC-γ1 and ras oncoprotein in carcinogenesis of laryngeal squamous cell carcinoma. The results are summarized as follows. 1) Among 15 laryngeal cancer tissues, 12 cases contained high level of PLC-γ1 and ras-oncoprotein compared to adjacent non-tumorous tissue. 2) All of 8 papillomas showed weak expression of PLC-γ1 and ras-oncoprotein. 3) There is a strong correlation in distribution of ras-oncoprotein and PLC-γ1. 4) According to degree of differentiation, poorly differentiated tumor revealed stronger staining compared to well differentiated tumor.