The efficiency with which llamas and sheep digest various roughages was compared in France in 1993. Six llamas (three of which were rumen-cannulated) and six rumen-cannulated sheep were simultaneously given three different diets: (i) a grass hay low in N content (HLN), (ii) the same hay with barley, representing 25% of the total dry matter (HLN+B) and (iii) a cocksfoot grass hay, rich i n nitrogen (HRN). Daily forage dry matter intake was slightly, but not significantly, lower in llamas (55·9 g/kg W0·75 ν. 60·3 g/kg W0·75 in sheep). Intake behaviour was similar for the two species except that the number of rumination periods was lower with llamas (P < 0·05). With all diets, the digestibility of both organic matter and cell walls (estimated from neutral detergent fibre) was higher in llamas (Animal Nutrition, 9700 Angra do Heroismo, Azores, Portugal 5+6 and +6+5 units respectively, P < 0·001). The higher digestibility in llamas may be related to the slightly lower level of intake and to the lower dry matter turnover rate in the forestomachs compared to sheep (3·9%/h ν. 5·3%/h, P < 0·01). However, in sacco degradation of both hays were higher in llamas' forestomachs after 24 h of incubation (+6+5%, P < 0·01) and 48 h (+4+3%, P < 0·05) than in sheep. The high microbial efficiency of the llamas can be ascribed to the physical and chemical characteristics of their forestomach contents, which had a higher liquid turnover rate (+1+4%/h, P < 0·05), a lower volatile fatty acid concentration (P < 0·01), a higher and more constant pH (P < 0·01) than in sheep and a greater buffering capacity when pH was close to neutral. These results suggest the greater ability of llamas to control the physicochemical conditions of their forestomach contents to digest cell walls efficiently and to minimize the negative effects of concentrate supplementation.