Observations were carried out in duplicate on two groups of six sows, that had been tethered individually, continuously during the first 24 h and then during feeding times, over a 4-week period. At this point two animals from one group were swopped for two animals from another group and the procedure was repeated. Contrary to the findings in the literature, in the first 24-h period after group forming, signs of reconnaissance outnumbered signs of aggression. This unexpected picture of little aggression just after group forming was also clear from the observations during feeding. The peak in the frequency of aggression only appeared in the third week. Simultaneously, there was a strikingly high correlation between threatening and running away; a very strong reaction. The results of the second period, after the exchange, show a different picture. In the first 24-h period, there was more aggression than reconnaissance. The level of aggression during feeding remained at the same level in time. The best correlation was found between threatening and a less severe reaction. Clearly, a period of individual housing causes sows to lose a part of their social skills. This could cause serious problems. However, a process of recovery is not totally out of the question.