Novel sol-gel synthetic techniques were used to immobilize copper-zinc superoxide dismutase (CuZnSOD), cytochrome c, and myoglobin (Mb) by encapsulation in stable, optically transparent, porous silica glass matrices under mild conditions such that the biomolecules retained their characteristic reactivities and spectroscopic properties. The resulting glasses allowed transport of small molecules into and out of the glasses at reasonable rates but nevertheless retained the protein molecules within their pores. Chemical reactions of the immobilized proteins could be monitored by means of changes in their visible absorption spectra. Silica glasses containing the immobilized proteins were observed to have similar reactivities and spectroscopic properties to those found for the proteins in solution. For example, encapsulated CuZnSOD was demetallated and remetallated, encapsulated ferricytochrome c was reduced and then reoxidized, and encapsulated met Mb was reduced to deoxy Mb and then reacted either with dioxygen to make oxy Mb or with carbon monoxide to make carbonyl Mb.