Natural variations in 87Sr/86Sr, /, /, and δ18O were used to investigate changing hydrologic flow paths during storm events in an 11.8 ha first-order watershed of the Hubbard Brook Experimental Forest. Throughfall, soil water, and stream water were sampled during several storm events and a single snowmelt event. Throughfall had 87Sr/86Sr, /, and δ18O values that were distinct from other water types. Soil water was highly variable in composition but could be separated into three distinct elevation zones in the watershed with 87Sr/86Sr and / both increasing with elevation in the watershed. Changes in 87Sr/86Sr, /, and δ18O of stream water during storm events yielded complementary information about watershed hydrologic flow paths. Traditional hydrograph separation using δ18O values indicated that new water was only a small component of storm flow (9--18%), whereas 87Sr/86Sr and / ratios indicated that shallow subsurface flow (soil water) contributed significantly to storm flow in amounts up to 40%, depending on soil moisture conditions.