The hydrolysis of glucose-6-phospate in the digestive gland of the crab Carcinus maenas is carried out by an aspecific phosphatase. This enzyme possesses the following features: (1) insensitivity to acid treatment; (2) absence of inhibition when exposed to citrate at low pH; (3) similar affinity for G6P as the acid phosphatase for Na-β-glycerophosphate (Km 2.3 and 2.0 m M, respectively). Glucose-6-phosphate and Na-β-glycerophate hydrolysis reactions seem to be catalysed by the same enzyme, since both activities exhibit the same distribution in a subcellular fractionation of the gland. Furthermore, as these activities are principally recovered in the subcellular fraction enriched in calcospherites (or calcium phosphate granules), it is proposed that the aspecific G6P-phosphohydrolase could play a major role in the formation of these granules. The phosphorylation of glucose is made by two "low Km" hexokinases (230 and 64 μM, respectively). As their level of activity shows significant changes over the moult cycle, these enzymes could be considered as having a regulatory role in the storage of glucose in the digestive gland.