Spherical beads have been prepared by ionotropic gelation of sodium alginate in the presence of CaCl2 and BaCl2 solutions and their swelling behavior has been studied. The barium ion-crosslinked beads exhibit almost minimum swelling of 40 +/- 3% in PBS at pH 7.4 but possess greater stability while calcium alginate beads exhibit nearly 160% of water uptake and subsequently dissolve. The beads appear to swell through ion-exchange process which was confirmed by monitoring the Ca2+ release from the calcium alginate beads. The release was found to be diffusion controlled. On treatment with 0.1 M HCl, the calcium alginate beads demonstrated a decrease in water uptake in PBS at pH 7.4 with faster degradation while for acid treated barium alginate beads, the water uptake was found to increase on treatment with HCl. When the two beads samples were put in media of continuous varying pH (to mimic the passage of beads from mouth to colon), barium alginate beads possessed greater stability, thus showing potential to be used for colon-targeted oral delivery. (C) 2004 Elsevier B.V. All rights reserved.