This article demonstrates the potential of encapsulated, engineered Lactococcus lactis as a vehicle for the oral delivery of therapeutic proteins. Using alginate-poly-l-lysine-alginate membrane-encapsulated L. lactis engineered to secrete the reporter protein Staphylococcal aureus nuclease, we show comparable viability and protein secretion between free and immobilized cells. After 12 h, microcapsules with a cell density of 4.8 x 10(5) colony forming unit (CFU) ml(-1) grew to 2.2 x 10(8) CFU ml(-1) and released 0.24 arbitrary unit (AU) ml(-1) of nuclease, producing similar results as free cells, which grew from 3.4 x 10(5) to 1.9 x 10(8) CFU ml(-1) and secreted 0.21 AU ml(-1) of nuclease. Moreover, encapsulated cells at a density of 4.4 x 10(7) CFU ml(-1) grew to 2.2 x 10(10) CFU ml(-1) in 12 h and secreted 15.3 AU ml(-1) of nuclease although 3.1 x 10(7) CFU ml(-1)of free cells reached only 2.3 x 10(9) CFU ml(-1) and released 5.6 AU ml(-1) of nuclease. We also show the sustained stability of the microcapsules during storage at 4 degrees C over 8 weeks.