Type IV collagen (COL-IV) interacts with a variety of cell types. We present evidence that human mesangial cells (HMC) bind directly to COL-IV, its major triple helical domain, and the main non-collagenous, NC1 domain. A synthetic peptide, HEP-III, and its triple helical counterpart (THP-III), previously reported to be a heparin-binding domain, also promoted ≈15% adhesion of HMC. HMC bound to solid-phase-immobilized, intact COL-IV (≈75%), isolated NC1 domain (≈15%), and a pepsin-derived triple helical fragment,which lacks Hep-III (≈65%). We further examined inhibition of HMC adhesion to COL-IV and its domains by using anti-integrin antibodies. Blocking monoclonal antibodies against the α2 integrin resulted in 70% inhibition of adhesion to COL-IV and 80% inhibition to HEP-III. Moderate inhibition was observed on the NC1 and triple helical fragments. Anti-α1 antibodies inhibited the binding of HMC to COL-IV, the NC1, and triple helical domains, but not to peptide HEP-III. Anti-β1 antibodies inhibited almost completely (>95%) the adhesion to COL-IV, the NC1, and triple helical fragments; inhibition on HEP-III was ≈30%. Affinity chromatography studies with solid-phase HEP-III and mesangial cell lysate also demonstrated the presence of integrin α2β1along with α3β1. We conclude that α2β1 and α1β1integrins mediate HMC adhesion to COL-IV. Peptide HEP-III is a major, specific site for α2 integrin-mediated binding of mesangial cells to COL-IV. Both the α1β1and α2β1 integrins interact with the NC1 and triple helical fragments of COL-IV. Therefore, we demonstrate that several sites for integrin-mediated interactions exist on several collagenous and non-collagenous domains of COL-IV.