Type IV collagen (COL-IV) interacts with a variety of cen 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 α2β1 along with α3β1. We conclude that α2β1 and α1β1 integrins mediate HMC adhesion to COL-IV. Peptide HEP-III is a major, specific site for integrin-mediated binding of mesangial cells to COL-IV. Both the α1β1 and 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.