Apparatus has been constructed to carry out precise measurements of rolling friction for rigid balls rolling over soft viscoelastic substrates, using a wide range of ball size, normal load, and rolling speed. Measurements are reported for two viscoelastic substrates, representing high and low energy loss elastomers. Measurements of the energy loss factor were also carried out for each substrate, using a simple rebound arrangement with a wide range of initial velocity and impact mass so that the contact time varied substantially. The rolling friction measurements were somewhat higher under all circumstances than the theoretical values, calculated using an energy loss factor appropriate to the contact time in rolling. The discrepancy at low rolling speeds was about the same magnitude as that reported previously by Greenwood, Minshall, and Tabor, and attributed by them to additional energy losses in complex strain cycles like those involved in rolling.