Three ruminally cannulated dry cows were used in an experiment designed as a Latin square to investigate the e †ects of amount and availability of starch on the amylolytic activity of ruminal solid-associated microorganisms (SAM). Animals were fed twice daily a diet (7 kg DM day~1) consisting of wheat straw, cocksfoot hay and ground barley in the ratios 10 : 90 : 0, 10 : 60 : 30 and 10 : 30 : 60. Nylon bags containing rapidly (barley) or slowly (maize) degradable cereal grains were incubated in the rumen. Enzymes of the SAM were extracted from rumen contents and bag residues, and amylolytic (amylase and a-D-glucosidase) activities were measured. The in situ degradation of starch was determined. Increasing the level of barley in the diet induced a linear increase in amylase activity of SAM in the rumen contents. In the bags, amylase activity and starch degradation rate were not modiÐed by supplementation. High activity was observed more rapidly in bags containing barley, where starch is rapidly available, than in bags containing maize, where starch is protected by a resistant endosperm. These results suggest that amylolytic activity of SAM may depend on the amount of starch available to microorganisms.