Seepage losses from animal-waste lagoons could affect ground water quality. Water balance methods were used to study seepage and nitrogen export from three swine-waste lagoons in southwestern Kansas, USA. Lagoons ranged in size from 0.8 to 2.2 ha and had an average waste depth of 5.6 m. Compacted-soil liners were 0.30 to 0.46 m thick and built with native soil or, in one case, a soil-bentonite mixture. Seepage was calculated from measurements of evaporation and changes in depth when the addition or removal of waste was precluded or quantified. Seepage rates were 1.1 , 1.1, and 0.8 mm d-1 from the three lagoons, with the lowest rate occurring at the site with a 0.46-m liner augmented with bentonite. The in-situ coefficient of permeability of the soil liners ranged from 7.8×10-8 and 1.5×10-7 cm s-1. In two lagoons built with silt loam liners (no bentonite), permeabilities on a whole-lagoon basis were about five times less than those measured from soil cores collected prior to the addition of waste. Results imply that permeability was reduced by organic sludge on the bottom of the lagoons. The average ammonium-N concentration in the lagoons was 665 mg L-1, accounting for almost all of the soluble N. Calculations indicate that the ammonium-N export rates were between 2187 and 2726 kg ha yr-1, but more information is needed regarding the fate of N deposited in the soil beneath lagoons.