Simple methods have been developed for encapsulating aqueous solutions of protein within polymer membranes. Stable microcapsules 1 to 100 micro in diameter, with semipermeable membranes, can be made by depositing polymer around emulsified aqueous droplets, either by interfacial coacervation or by interfacial polycondensation. Aqueous suspensions of enzyme-loaded microcapsules act well on small-molecular substrates both in vitro and in vivo.