The substrate specificity of snail, limpet, and bovine glucuronidases was examined by using p-nitrophenyl glucuronide and p-nitrophenyl 6-O-sulfo-D-glycopyranosides as the glycosyl donor and acceptors, respectively. When the donor was treated with these enzymes in the absence of the acceptors, beta(1-3) glucuronyl disaccharides were obtained as the major products together with beta(1-2) isomers as the result of an enzymatic "self-transglycosylation"reaction.