We have constructed NS0 myeloma cell lines that inducibly express the p21(CIP1) cyclin dependent kinase inhibitor, using the Lacswitch system. Ectopic p21(CIP1) protein expression was rapidly induced within 12 h of addition of IPTG, causing G1-phase arrest and almost complete inhibition of cell proliferation. The production of a chimeric IgG4 antibody, expressed constitutively from an independent promoter, was found to be significantly increased by more than 4-fold in p21(CIP1)-arrested cells. This study demonstrates for the first time the successful construction of anchorage-independent and proliferation-control led NS0 cell lines with enhanced secreted chimeric antibody production independent of the inducible promoter activity used to achieve cytostasis.