[en] The unsaturated zone at Yucca Mountain, Nevada, is being evaluated as a potential repository for high-level nuclear wastes. Estimates of ambient moisture tension, effective hydraulic conductivity, and vertical flux are needed to design additional investigations and to develop preliminary models of the geohydrologic system. In deep unsaturated zones of uniform properties, hydraulic-head gradients are unity, and effective hydraulic conductivity may be used to estimate vertical flux. Analyses were made on 19 core samples of unsaturated tuff from test well USW H-1. Moisture-characteristic curves relating saturation and moisture tension were developed from results of mercury-injection tests. Ambient moisture tension estimated from these curves generally was 100 to 200 kilopascals. Values of relative permeability ranging from about 0.002 to 0.1 were determined by fitting an analytical expression to eight of the moisture-characteristic curves, and then integrating to solve for relative permeability. These values of relative permeability were applied to values of saturated hydraulic conductivity of core from a nearby test well to obtain effective hydraulic conductivities of about 8 x 10^-12 to 7 x 10^-10 centimeter per second. If a unit hydraulic-head gradient is assumed, these values convert to a vertical flux through the tuff matrix of 0.003 to 0.2 millimeter per year. The validity of this assumption was not verified due to the sparseness of data and uncertainties in their reliability. Consequently, the results of this study are preliminary and need to be used only as a guide for future studies. 9 references, 30 figures, 1 table