This paper is the first report of the use of a fluorescent indicator (Dextran-coupled calcium green-1) for imaging of cytosolic free calcium in ciliate cells. Using this technique in Paramecium, we show that a very transient increase in the mean intracellular calcium concentration accompanied exocytosis. It has long been postulated based on indirect experimental evidence, that a calcium wave which would spread across the cortex at the time of cell division, would be the primary event that triggers morphogenesis in these species. We theoretically show that a unifying interpretation can be given for the possible occurrence of a single wave and that of multiple oscillations of cytosolic calcium: both of which correspond to two different behaviors of the same dynamic system. Experimental conditions allowing the visualization of possible calcium periodicities in the interphase Paramecium cell are much more easily fulfilled than those permitting the observation of a single wave at the time of cell division. Hence, experiments were performed on interphase cells. After microinjection of calcium indicator into a mutant strain which is defective in exocytosis, we observed Ca2+ oscillations with a period close to 2 minutes. Hence, we conclude that Paramecium possesses all the dynamic elements required to generate, at the time of cell division, a morphogenetic calcium wave.