We examined the activity of Griffonia simplicifolia II agglutinin (GS2) before and after neuraminidase treatment in 2 cases of primary benign mixed tumor (BMT) and a case of recurrent mixed tumor (MT). Histologically, each type of MT is comprised of epithelial and mesenchymal components. GS2, which showed no binding to either structural component in the primary BMT, was specifically bound to the mesenchymal component in the recurrent MT. After neuraminidase treatment, there was a marked increase in GS2-binding levels in the epithelial component of the primary BMT and in both components of the recurrent MT. These results might reveal a prominent sialylation in the recurrent MT.