The influence of surfactant on the deformation of a viscous drop in a uniaxial extensional flow is considered. Previous studies (1, 2) have examined the role of insoluble surfactant. Here, we examine soluble surfactant, i.e., surfactant that may be transferred between the interface and the continuous phase. The transfer of surfactant to and from the interface mitigates many of the effects observed with insoluble surfactant by diminishing the magnitude of surfactant gradients. In the presence of soluble surfactant, the deformation generally lies between that of insoluble surfactant and that of a drop with a constant and uniform coverage of surfactant. However, there are notable exceptions particularly at high surfactant activity. The influence of surfactant on the interfacial velocity of the drop is also explicitly considered. It is shown that while insoluble surfactant can substantially retard a drop interface, interphase surfactant transfer acts to remobilize the interface.