The total amounts of time spent eating and ruminating per 24 h by goats and sheep were determined. The efficiencies of chewing during eating (<C.EAT>) and chewing during ruminating (<C.RUM>) on the breakdown of feed particles to below the critical size required to leave the rumen (< 1.0 mm) were investigated. All studies were done with the animals fed on a chaffed lucerne (Medicago sativa) hay diet. Goats spent more time eating (+3.1 h; P < 0.01), and less time ruminating (-2.2 h; P < 0.05) per 24 h, than sheep, when fed hourly at ad lib. intake. The efficiency of chewing during eating (<C.EAT>) in breaking down feed particles to < 1.0 mm was greater in goats (85%; P < 0.01) than sheep (48%). The process of rumination in sheep served to reduce the feed particles which were > 1.0 mm in the rumen to < 1.0 mm. Sheep tended to be more efficient in this process than goats (59 ν 48%), with the difference not attaining significance (P > 0.1). The greater frequency of chews (number of total jaw movements/min) during eating in goats (P < 0.01), or during ruminating in sheep (P < 0.001), was the major component explaining differences in efficiency between the two species in both the eating and rumination processes. When corrected for the number of chews/min, the differences in <C.RUM> and <C.EAT> were not significant between goats and sheep. During eating goats had greater apparent rates of total salivary secretion (P < 0.1), and greater apparent rates of salivary nitrogen secretion (P < 0.05) than sheep. The results help explain the greater fibre digestibility and rumen ammonia irreversible loss rates in goats than sheep, when both species were fed on lucerne chaff.