Within about 10 seconds after stimulation of Dictyostelium discoideum cells with cyclic AMP an increased rate of 45Ca influx was observed. Part of the cellular calcium reappeared in the extra-cellular medium between 1 and 3 minutes after stimulation. No effect of 5'AMP on calcium distribution was found. The transient calcium influx is discussed in connection with chemotaxis and other cyclic-AMP induced responses.