The nephrin-slit diaphragm protein complex contains a group of scaffolding proteins that function to connect junctional membrane proteins to the actin cytoskeleton and signaling cascades. By mass spectrometry four of the proteins identified, alphaII spectrin, betaII spectrin, alpha-actinin, and IQGAP1, represent adherens junction-associated proteins, and two, MAGI-2/S-SCAM and CASK, represent MAGUK family scaffolding proteins that associate with Ig superfamily proteins. The presence of these proteins in slit diaphragms and their association with nephrin suggests that they may form a scaffolding protein complex in the podocyte slit diaphragm and thus contribute to the regulation of ultrafiltration by binding slit membrane proteins and establishing their cytosolic connections.