gamma-glutamyl transpeptidase(gamma-GT) activity of cells from esophageal abrasive balloon cytocollection in 150 outpatients was detected and the characteristics of gamma-GT positive cells were studied in 107/150 cases. The gamma-GT positive cells may have been squamous cancer cells, dysplastic, hyperplastic or normal epithelial cells seen simultaneously or individually on a smear. The normal intermediate and superficial layer cells with positive gamma-GT were very frequently observed on the positive cytological smears. The hyperplastic and dysplastic cells were less frequently observed on the smear as compared with that of the high incidence area. Of 150 specimens, no cancer cells or gamma-GT activity was detected in 35; gamma-GT positive cells were observed in 70 out of 73 positive smears (95.9%); negative cancer cells and gamma-GT positive cells were seen in the rest 42. 25 of these 42 patients were followed and 19 became diagnosed as esophagus cancer by repeated abrasive balloon, biopsy or X-ray examination. It is suggested that the persistent gamma-GT strongly positive cells be a signal of the existence of cancer. In other words, gamma-GT detection on the smears can be used as an adjuvant parameter in cytology to improve cytological diagnosis.