A method of immobilizing urokinase on albumin microspheres has been developed. Laser scattering, which was used to follow particle size from the initial emulsification stage to the final aqueous resuspension of the microsphere stage, showed that particle coalescence and crosslinking were critical parameters in manufacturing the microspheres. Chemical dehydration with 2,2-dimethoxypropane was used to convert an albumin emulsion into an albumin suspension and to reduce coalescence. An optimal amount of dehydrant produced 0.3-micron particles which resisted a 50 degrees C temperature challenge. Since oil/glutaraldehyde emulsion resulted in large particles with no urokinase activity, the cross-linking concentration of glutaraldehyde was reduced by solubilizing 25% (w/v) glutaraldehyde in the oil phase with n-propanol. A concentration of 0.015% (v/v) glutaraldehyde effectively immobilized urokinase and stabilized albumin microspheres. Amidolytic activity using the specific chromogenic substrate for urokinase, S-2444, showed that enzyme activity could be retained during this glutaraldehyde cross-linking.