Scientific activities of alpha- and beta-galactosidases and alpha-and beta-glucosidases in crude homogenates of the digestive gland and gut tissues of Callinectes sapidus (Rathbun) were measured. Maximal specific activity occurred at pH 4 when homogenates were tested against four artificial substrata. Activity occurred at pH 4-8. Rates of hydrolysis were consistently high (8.8-10.6 nmol substratum hydrolyzed·min-1·mg-1 total protein) for artificial substrata (p-nitrophenyl-alpha-d-galactopyranoside, p-nitrophenyl-beta-d-galactopyranoside, p-nitrophenyl-alpha-d-glucopyranoside, p-nitrophenyl-beta-d-glucopyranoside). When natural substrata (melibiose, lactose, sucrose, maltose and cellobiose) were tested with digestive gland homogenates, appreciable enzymatic activity (specific activity 0.041) was detected for maltose. This disaccharide is a component of starch (alpha-1,4-glucan), one of the primary complex storage sugars in vascular plant tissues. These data indicate that C. sapidus may have the physiological capacity to utilize vascular plant material (e.g., starch), a common component of detritus within coastal estuaries and bays. Although detritus has been observed in the guts of both juvenile and adult C. sapidus, the capacity to use detritus may be particularly important to juvenile blue crabs which use vegetated areas as refuge and may have limited abilities to capture and ingest live animal prey. © 1991.