A model microparticulate carrier system, capable of partially protecting an entrapped antigen against enzymatic degradation, has been successfully used to induce an enhanced secretory immune response to an incorporated model soluble antigen following oral administration to experimental rats. Ovalbumin was incorporated into polyacrylamide microparticles (2.55 microns diameter) and administered orally on four consecutive days to rats primed 14 days earlier by intraperitoneal injection. The memory secretory IgA antibody response (day 65) to the microparticle incorporated antigen group was significantly raised relative to a soluble antigen control group response (p less than 0.01), following administration of a booster dose of soluble antigen to both groups (day 61).