Abstract 1. 1. Both qualitative and quantitative studies have been made on the distribution and content of glycogen in seven monogenetic and eight digenetic trematode species. 2. 2. Glycogen occurs predominantly as intracellular deposits in the parenchyma in all species with smaller amounts associated with the musculature and reproductive complex. Species differences exist regarding the relative amounts of glycogen deposited in the various tissues. 3. 3. Quantitative data support the view that the nature of the parasitic habitat influences the amount of carbohydrate stored by a particular species but other factors, such as the nutritional state of the host, appear to be involved.