1. Cells ofDictyostelium discoideum grow exponentially when cultivated in suspension. The generation time is 3,3 hrs (20° C). 2. In all stages of their development the cells can agglutinate spontaneously. Agglutinates in a certain developmental stage undergo immediate transformation into fruiting bodies, if they can make contact with the liquid/air interphase. This contact induces the polarity of the fruiting bodies. Autonomous polarization does not occur. Bilateral interphase contact induces twin fruiting bodies pointing in opposite directions. 3. Weakening of intercellular contacts results in a reduction of the average size of the agglutinates and can thus be recognized easily under standardized conditions. This was shown to be the case for two morphologically deficient mutants.