The morphogenetic capacities of cells inDictyostelium discoideum, as well as of groups (agglutinates) of these cells are changed in a constant time course after food consumption has been stopped.Two questions were posed: 1. When is the capacity of aggregation at its maximum level in a culture of single suspended cells. 2. At what time do agglutinates answer an external stimulus immediately by establishing polarity.The maximum of aggregation capacity lies 8-10 hours after complete food exhaustion. This functional stage is cytologically characterized by accumulation of metachromatic granules in the cells [seeBONNER et al. (1955)]. - The polarization capacity of agglutinates depends primarily on the functional age of the cells (this means that the age of the cells is related to the time of complete food exhaustion), and secondly it depends on the age of the agglutinates. In the most favorable case the maximum response is reached 12 hours after complete food exhaustion.A difference of about 2 hours lies between the beginning of aggregation and polarization. This difference in time could explain the centerless aggregation patterns of a well synchronized cell population as well as the appearance of primary aggregation centers in non-synchronized cultures.