During the time course of differentiation in Dictyostelium discoideum, glycogen was found to accumulate from the amoebae stage to the culmination stage of development. Upon sorocarp formation (23 h), glycogen was rapidly degraded. Ultramicrotechniques, utilizing amplification of glycogen by enzymatic cycling, were used to follow glycogen metabolism in pre-stalk and prespore cells during the differentiation cycle. Both cell types accumulated glycogen at nearly the same rate. By the pseudoplasmodium stage of development glycogen had accumulated to 50% of its maximum value, and no differences were found between pre-stalk and pre-spore cells. Glycogen was degraded as pre-stalk cells migrated into the position for stalk construction. At the culmination stage of development stalk cells near the base were devoid of glycogen while pre-stalk cells near the apex of the stalk showed no loss of glycogen. The complete loss of glycogen from stalk cells occurred over a distance occupied by approximately 100 cells, and over a time period of approx. 1 h. Pre-spore cells at the culmination stage showed no loss of glycogen even though separated from stalk cells by only a thin cellulose sheath. The degradation of prespore cell glycogen did not commence until stalk construction was completed and the pre-spore mass had reached the apex of the stalk. Pre-spore cells at the culmination stage contained high levels of glycogen while only 2 h later, total degradation had occurred.