Transmission losses through the beds of hillslope rills were studied at two sites in the semi-arid southwestern U.S. At one site the rills were sand-bedded and at the other they were gravel-bedded. Transmission losses in the sand-bedded rills are about 66% higher than those in the gravel-bedded rills. The former show evidence of increasing transmission loss with increasing depth of flow, whereas the latter do not. In both cases, transmission losses in the rills are about an order of magnitude greater than infiltration losses in adjacent interrill areas. Copyright © 1999 John Wiley & Sons, Ltd.