The aim of this study is to develop multilayer beads with improved properties for controlled delivery of the antibiotic ampicillin. Ionotropic gelation was applied to prepare single and multilayer beads using various combinations of chitosan and Ca(2+) as cationic components and alginate and polyphosphate as anions. Beads prepared with higher concentrations of chitosan entrapped more ampicillin. During incubation in simulated gastric fluid, the beads swelled and started to float but did not show any sign of erosion. Single layer chitosan-alginate beads released 70% of the drug within 4 h. Multilayer beads released only 20-30% in the same period of time. During subsequent incubation in simulated intestinal fluid, both single and multilayer beads continued to release drug. At least part of this release is due to disintegration of the beads. The rate of release both in gastric and intestinal fluid and the kinetics of disintegration in intestinal fluid can be controlled by changing the chitosan concentration in the coagulation fluid. The release of the drug can also be controlled by the degree of cross-linking using polyphosphate. Cross-linked multilayer beads were prepared that released only 40% of the entrapped drug during 24 h. It is concluded that chitosan-alginate multilayer beads, cross-linked with polyphosphate offer an opportunity for controlled gastrointestinal passage of compounds with low molecular weight like ampicillin.