Most procedures to measure the hydraulic conductivity of slowly permeable materials such as compacted soil liners are based on analyses that assume saturated, one-dimensional flow under steady-state conditions. The overwhelming problem, however, is the very long times, of the order of weeks or months in liner materials, to reach experimentally-measurable steady flow. A new field procedure is proposed for slowly permeable materials that takes advantage of the early transient flow in initially unsaturated soil. Both constant head and falling head techniques are proposed and measurement times are of the order of one half to several hours. The falling head technique has the advantage of requiring only the difference between the field-saturated and initial water contents in addition to the measured position of the falling head above the soil surface as a function of time. An experiment on the experimental soil liner at Champaign, Illinois, gave saturated hydraulic conductivity values using the constant head technique that were in good agreement with previously measured values. A laboratory test demonstrates the advantages of the falling head technique.