The nuclear track technique, which can be used to measure concentrations of radon directly, can also be employed to determine radon flux by means of gradients in concentration in the ground, at its surface, or above the surface. Diffusional properties or emanation properties need to be assesed, but often can also be measured by track counting. Measurements at Thoreau, New Mexico give a flux of 1.4 atoms/cm2-s over an area of 60,000 m2. At Scotia, New York, 1.1--1.2 atoms/cm2-s are measured over an area of 100 m2.