A new method is being developed for the in-situ measurement of shear wave velocity, V^s, in the soil surrounding a borehole. The method involves the measurement of axially propagating surface waves inside an uncased borehole using the Spectral-Analysis-of-Surface-Waves (SASW) approach. Testing is performed with instrumentation housed inside an inflatable tool. Inflation pressures applied by the tool are used to vary radial stresses in the soil surrounding the borehole. Surface wave velocities over a range of frequencies are measured at each inflation pressure. These measurements are then theoretically modeled so that the variation in V^s (and hence small-strain shear modulus, G^max) with distance behind the borehole wall is determined at each pressure. The results of field tests with the borehole SASW tool at two sites composed of unsaturated clayey soils are presented. These results are compared with independent field seismic measurements and with laboratory tests on intact specimens using the torsional resonant column to assess the validity of the new field method.