The roughage intake capacity of cows is discussed in relation to results based mainly on experiments with high-yield cows during 1964-1969. Most of the experimental groups were given grass silage to appetite, in some cases together with fixed amounts of hay and root crops as well as concentrates according to requirements. Details are given of roughage intake in relation to body wt., silage quality and period of lactation. When 1 kg hay was fed plus silage ad lib., there was a highly significant negative correlation (r = -0.66) between roughage intake (DM/100 kg body wt.) and daily 4%-FCM yield in weeks 2-10 of lactation, but a positive correlation between roughage intake and week of lactation during the same period. In weeks 14-35 of lactation, however, these correlations were reversed (r = +0.30 between intake and FCM yield). Roughage intake was highest 16 wk after calving, when daily milk yields were 24-26 kg. Data are given on the effect of feeding concentrates and root crops on roughage intake.