Two studies were conducted to test the effects of stall design on cow behaviour and comfort. In the first study 16 cows were housed in stalls with concrete floors or mattress flooring. When on mattress floors the cows spent 1.8 h more time lying each day. However, cows had fewer lying bouts on the concrete, but they were longer than for those on mattresses. Cows on mattresses stood up lay down more often than on concrete. Cows spent similar amounts of time eating and consumed similar amounts of feed on both surfaces. The data were interpreted to indicate that cows on concrete found it more difficult to change postures than did those on mattresses, and that the concrete was less comfortable. In the second study the cows were housed in stalls with either a narrow or wide front opening to the stall. Cows in the wide opening spent more time with their head in the manger area, a posture that was facilitated by the stall design. However, again there were no differences in eating time or consumption. It was concluded that mattresses were an effective means of improving cow comfort in lactating dairy cows.