The primary concern has been focused on the response and adaptation of mouse fibroblast tumor cells to heat-shock in the level of membrane surface proteins, using two labeling techniques, lactoperoxidase-catalyzed iodination and galactose oxidase-sodium borohydride. Cells arrested in $G_1$ phase exhibited the highest level of LETS protein and high molecular proteins than did cells passing through $G_1/S, S, G_2$ and M, and unsynchronized cells. Confluent cells were found to show an increase in 125K proteins and a decrease in 130K and 100K proteins selectively. The adaptation processes of tumor cells after heat-shock were observed. All the proteins above 80K were reduced immediately after heat-shock, whereas 70K protein increased markedly 24 hours after heat-shock. The 70K protein and high molecular proteins returned to normal level in 48 hours. The 70K protein was found to be trypsin-sensitive and was similarly labeled by galactose-oxidase as well as by lactoperoxidase. It was, therefore, concluded that 70K protein is glycoprotein located on the surface membrane and might be the HSP 70. Possible function of heat-shock protein on the surface membrane and the relation of this protein to differential heat-sensitivity of tumor cells are discussed.