Entrapped cells of P. diminuta were used for the production of 7-aminocephalosporanic acid (7-ACA), a key intermediate required for the production of most of the clinically used cephalosporin derivatives, i.e., semisynthetic cephalosporins. The repeated batch production of 7-ACA with entrapped cells of P. diminuta in different carriers were carried out for six cycles at optimal conditions. It was found that 33%, 38%, and 47% of activity was lost with chitosan, gelatin, and agar, respectively as immobilizing supports after the sixth cycle of operation.