The behaviour of 28 domestic cats from the 4th to the 12th weeks after birth was studied in the presence and absence of their mother. We obtained measures of distress, activity, timidity, distance between mother and kitten, and seven facets of play. The developmental trends in the various measures of play were different, some categories declining in frequency from the 4-7 week period to the 8-12 week period and others notably Object Contact, increasing markedly. These opposing trends and a marked lack of correlation between the measures of play suggest that the outputs of several independent systems are commonly lumped under the general heading of play. The measures of more general aspects of behaviour did not show analogous trends to any of the measures of play and were not correlated with any of them. Cat Contacts in the 4-7 week period was a strong predictor of the same measure in the 8-12 week period. However, none of the other correlations between play in the two age periods is statistically significant, emphasising the marked developmental discontinuity, shown particularly in Object Contacts, between seven and eight weeks after birth. Males made significantly more Object Contacts than females in the 8-12 week period. However, this difference was much less marked when the females had a male in the litter.