Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Calliandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) to sheep (n \ 3) given a basal diet of barley straw ad libitum. Tree leaves were fed either freshly harvested (F \ fresh) or after drying at 60¡C in a forced draught oven (D \ dried). Voluntary intakes, digestibility and aspects of nitrogen (N) and phenolic compound metabolism were measured in all sheep. Drying decreased the condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg~1 DM). Total phenolics (TP) were signiÐcantly decreased when Gliricidia was dried (F 39, D 21 g TP kg~1 DM), and CT content was reduced from 20 g CT kg~1 DM to zero. Sheep given Gliricidia had higher rumen ammonia concentrations (73È 85 mg N litre~1) than did sheep given Calliandra (37È40 mg N litre~1). For both species, drying signiÐcantly increased the voluntary consumption of straw, increased DM digestibility, decreased faecal N excretion and increased N balance. For calliandra, drying decreased the apparent degradability of N in the rumen (DNR) from 0É40 to 0É28 g N g~1 N ingested, and increased the apparent digestibility of N (ADN) in the post-ruminal tract from 0É20 to 0É52 g N absorbed g~1 N Ñowing into the small intestines. For Gliricidia, DNR decreased from 0É64 to 0É51 and ADN increased from 0É41 to 0É56. There were no signiÐcant e †ects of drying on rates of microbial N synthesis. The above changes were discussed in relation to changes in tannin content and it was concluded that drying facilitates the formation of proteinÈtannin complexes which protect proteins from degradation in the rumen. These proteins are subsequently released in the small intestines, thereby promoting an increased efficiency of dietary N utilisation.