A continuous biparticle fluidized-bed reactor (BFBR) is developed for the simultaneous fermentation and recovery of lactic acid. In this processing scheme, bacteria are immobilized in gelatin beads and are fluidized in a columnar reactor. Solid particles (weak-base resin IRA-35) with sorbent capacity for the product are introduced at the top of the reactor and fall countercurrently to the biocatalyst, effecting in situ removal of the inhibitory lactic acid while also controlling reactor pH at optimal levels. One-week-long fermentation trials using immobilized Lactobacillus delbreuckii with sorbent addition demonstrated a volumetric productivity (6.9 g/L . h) at least 16-fold higher than that of a free-cell batch fermentation with base pH control and identical biomass concentration and medium composition. Regeneration of the loaded sorbent from the BFBR has effected a 35-fold concentration of lactic acid compared with original levels in the fermentation broth (70 vs 2 g/L). Lactic acid concentrations as high as 610 g/L have been observed when the loading solution contained 50 g/L lactic acid. Rich medium formulations did not seem to increase BFBR performance. The benefits of this reactor system, as opposed to conventional batch fermentation, are discussed in terms of productivity and process economics.