1. The kinetic mechanism of beta-glucosidase (beta-D-glucoside glucohydrolase, EC 184.108.40.206) of Botryodiplodia theobromae Pat. has been studied in the presence of competing glucosyl acceptors. 2. Glycerol, fructose, sucrose, cellobiose and to a much lesser extent, maltose can act as glucosyl acceptors, apart from water. 3. Evidence confirming and supporting the kinetic mechanism previously postulated (Umezurike, G.M. (1971) Biochim. Biophys. Acta. 250, 182-191) is presented. 4. A theoretical kinetic analysis of the behaviour of the enzyme in the presence of two alternative glucosyl acceptors in addition to water is found to be consistent with experimental observation, suggesting a system in which both donor and acceptors bind to the enzyme in a random fashion to form ternary complexes. 5. The results are discussed in terms of the mechanism of group-transfer reactions.