We have previously shown virus particles encapsulated in aqueous spermine alginate constructs retain immunogenicity and infectivity both in vitro and in vivo. However, because virions are complex structures with multiple reinforcing components, it was uncertain if isolated single proteins would retain functional integrity when similarly encapsulated. To examine this question trypsin, used as a model protein, was blended with aqueous sodium alginate and the blend was dispersed as fine droplets in aqueous spermine hydrochloride to generate self-assembling, trypsin-containing microcapsules. Trypsin was assayed spectrophotometrically for retention of enzymatic activity using N-alpha-p-tosyl-L-arginine methyl ester as substrate. Neither of the encapsulating reagents alone inhibited enzyme activity. Enzyme that escaped capture was assayed directly in the manufacturing supernatant. Tn mass balance studies we found that about 20-30% of activity was retained in intact capsules with the remainder resident in the aqueous manufacturing supernatant and washes. However, we found that the capsule wall appeared to inhibit enzyme activity by retarding substrate diffusion into and product diffusion out from the capsules, as evidenced by an increase in activity on lysis. Thus, it is clear that a single protein, as represented by trypsin, can retain functional integrity when encapsulated in this all aqueous system.