The diurnal variations in the specific activities of polysaccharide‐degrading enzymes after feeding were monitored in adherent and non‐adherent microbial populations separated from bovine rumen liquor and digesta solids. There were marked differences in the activity profiles of the enzymes within the subpopulations. Enzymes involved in the degradation of soluble carbohydrates were more active in the non‐adherent populations, and in the liquor phase subpopulation activities increased in the 1–2 h post‐feed period. The muralytic enzymes were most active in the adherent population. Specific activities increased by up to 20‐fold over the 24 h period, with an initial five‐fold increase occurring between 8 h and 12 h after feeding. Enzyme levels in the three non‐adherent populations were similar at the end of the postprandial period. In the population recovered from the liquid associated with the digesta particles, however, the activities did not increase until the latter stages of the period, whereas in the non‐adherent population from the digesta solids the activities varied little during the diurnal cycle. The numbers of micro‐organisms associated with the digesta solids were similar at 2 h and 20 h after feeding; the variations in enzyme levels did not occur as a result of a population increase but were due to increased activities in an established population. The plant cell wall structural polysaccharides were degraded at different rates. There was no appreciable cellulose digestion during the first 8 h of the postprandial period and although hemicellulosic constituents were removed continuously the rate of loss of both polymers was increased in the later stages of the diurnal cycle when enzyme acti