Abstract: To analyze the expression of loss of hererozygosity (LOH) of tumor DNA and plasma DNA, and to investigate their relations. To explore the value of microsatillite change of plasma DNA on the early diagnosis, screening and followup. Methods: Fortythree cases of laryngeal cancer treated surgically were analyzed. Preoperative and postoperative blood (10 ml), tumor tissue, paratumor tissue were collected. The lymphocyte and plasma were separated. And the DNA was extracted respectively. Three loci with high occurrence, D9S162, D9S1782 and D17S1665 were selected, and the primer was projected and composed. The electrophoresis was analyzed with ID Image Analysis Software. Results: The LOH incidence of tumor, preoperative plasma, postoperative plasma for D9S162 was 51.85%， 44.44% and 33.33%； for D9S1782 was 43.48%, 39.13% and 34.78%； and for D17S1665 was 51.43%, 42.86% and 37.14% respectrively. LOH of 6 loci disappeared. There was no significant difference for LOH between early and advanced laryngeal cancers（P＞0.05）.Conclusions: The plasma LOH expression is coincident with the tumor.

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