CD44 is a cell surface receptor for hyaluronan which affects cell adhesion and migration, and has been implicated in chronic inflammation and in tumorigenesis. To elucidate the molecular mechanisms underlying its multiple functions, we used a peptide-based pull-down assay to identify proteins that interact with CD44. Nonphosphorylated or phosphorylated peptides from the intracellular CD44 C-terminus, were immobilized and used as baits. Interacting proteins were subjected to SDS-gel electrophoresis and were identified by MALDI-TOF mass spectrometry. Several interaction partners were identified, including proteins involved in cytoskeletal reorganization, transcription, endocytosis, and intracellular transport. An endogenous complex between CD44 and one of the interacting proteins, the actin binding protein IQGAP1, was demonstrated in several normal and transformed cell types.