Losses due to leaching by rain were measured in laboratory experiments with simulated rainfall. The experiments included both conditioned forage and macerated forage mats. Four species, two grasses and two legumes, with three different cutting dates were used in the trials. Variables studied were: rainfall amount; rainfall intensity and dry matter content at the time of rainfall. Leaching losses showed a declining rate of increase with increasing rainfall amounts. Loss levels were significantly higher for mats. For conditioned forage, the results showed a significant trend towards higher losses with increasing dry matter content at the time of rainfall. In the case of mats, losses were smaller for mid-range dry matter contents, compared with both drier and wetter mats. Differences between species were rather small for conditioned forage. On the other hand, loss levels for mats varied considerably between species, with significantly higher losses for legumes than for grasses. A leaching loss equation is suggested which includes rainfall amount, dry matter content at the time of rain, species and conditioning treatment as variables.