Surface complexes of Ig-anti-Ig (Ig, immunoglobulin) readily redistribute into caps. Local anesthetics (lidocaine and chlorpromazine) disrupt the caps, the complexes disseminating over the entire surface. Removal of the anesthetic then allows the complexes to reform into caps. The effects of the anesthetics on cap disruption were counteracted by an increase in extracellular Ca2+ and were not energy dependent. The inhibition of cap formation by anesthetic is also counteracted by increased extracellular Ca2+.