Enzymatic activity observed in low moisture systems has been analyzed from several standpoints. The rates of enzymatic reactions depend on many factors, the molecular mobility of the reactants and the properties of the matrices in which they are embedded (pH, viscosity, ionic strength) being often controlling aspects. The objective of present work was to investigate beta-galactosidase activity as affected by pH-moisture dependence and by physical properties of the matrix in reduced moisture systems of whey (W) and dextranes (Dx). Beta-galactosidase from 3 different sources, Escherichia coli, Aspergillus oryzae, and Saccharomyces lactis, were tested. Beta-galactosidase activity from S. lactis was reduced in W systems. pH-moisture dependence was proposed as the main cause of this low activity. The decrease of apparent pH upon water removal and the molecular mobility of the polymeric matrix, and of the enzyme, which is related to their size, appear to be more significant factors than the actual value of the glass transition temperature (T-5) of the matrix on beta-galactosidase activity. Therefore, all properties concerning physico-chemical aspects have to be considered to analyze enzyme activity in low moisture biomaterials.