Leaching of soluble substances may be an important first step in leaf litter decomposition in small streams, but recent research has suggested that large leaching losses (up to 30% of initial mass in 48 h) may be an artifact created by using air-dried leaves in decomposition experiments . In laboratory experiments, we compared 3 d leaching losses from freshly fallen and air-dried senescent leaves of 27 tree species from different regions across Canada . Air-dried leaves from all species leached measurable amounts of original mass (3 .6-32 .8% dry mass), but leaching losses from fresh leaves (0-35%) were detectable in all but two species . Air-drying increased leaching losses in many species, but in others it reduced leaching losses or had no measurable effect . Results for leaves of the same species collected in different regions or in different years were generally similar, but species within the same genus often behaved very differently . Neither moisture content (fresh or air-dried), leaf thickness, nor cuticle thickness proved of any value as predictors of leaching losses or the effect of air-drying . The propensity of autumn-fallen leaves to leach, whether fresh or air-dried, appears to be a property of the individual tree species .