Sows are exposed to stress when constituted into newly formed groups. The stress observed is very similar to that of pigs after transport and before slaughtering. The sows' stress owing to grouping may result in fertility problems and, in extreme cases, even lead to death. A study has been conducted to reduce stress owing to grouping and its consequences for sows. The following procedures may assist in reducing stress at grouping. Firstly, the size and shape of the pen should allow frightened sows the opportunity to escape from aggressors. Secondly, the optimum number of sows for grouping, or the minimum number to be added to an existing group, should be determined. Thirdly, the best timing, in relation to the breeding cycle, for minimizing fertility problems needs to be identified. Fourthly, straw should be available in order to reduce aggression. Fifthly, sows should be observed for signs of excessive stress. Sixthly, the most suitable technical equipment, such as computerised feeding stations, needs to be determined. Finally, use of the best available management techniques should ensure optimum environmental conditions. Ethological design of a practicable farrowing pen H. Schmid Universittit Ziirich, Nutztierethologie, Ziirich, Switzerland Abstract In conventional farrowing systems, the problems of low labour and low piglet losses byIn conventional farrowing systems, the problems of low labour and low piglet losses by