Hydrogen peroxide was incorporated into silica xerogel matrix over the concentration range from 3.8 to 68.0 wt% via the sol-gel route. The obtained composites were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The release rates of H(2)O(2) from the composites into the aqueous phase were examined. In most cases, a 90% release was attained after ca. 10 min, and it was only slightly dependent on H(2)O(2) concentration and particle size. The antimicrobial activity of the composite containing 3.59% H(2)O(2) was evaluated against Escherichia coli and Micrococcus luteus. A comparative assay was carried out for aqueous solution of H(2)O(2) of the same concentration. The results demonstrated a potent microbicidal efficacy of the composite. Furthermore, diffusion range of the hydrogen peroxide from the solid composite into an agar medium matched that of the H(2)O(2) in aqueous solution. The stability tests with the xerogels containing 3.8, 26.4, and 68.0% of H(2)O(2) showed that after 63 days respective losses of the H(2)O(2) at 3 degrees C were 8.8, 9.7, and 6.2%. Both the DSC results and the stability tests have shown that the molecular water present in the pores stabilizes the composite, probably through improving the binding of the H(2)O(2) molecules onto the silica surface.