The denitrifier, Pseudomonas stutzeri, entrapped in chitosan beads, was incubated under denitrifying conditions in a column receiving a continuous supply of full-growth medium. Biochemical, structural, and mechanical properties of the beads were studied during the first 11 days of incubation; nitrate removal was followed for 45 days. Under these conditions they contracted and became lighter with time. Contraction was not uniform in all planes. Mechanical compressive properties of beads strengthened over the first 9 days and weakened thereafter. Concommittantly, structural changes of the beads were observed; denitrification and nitrite accumulation were lower in entrapped than in free cells.