A mixture of laminin and type IV collagen was analyzed by rotary shadowing using carbon/platinum and electron microscopy. Laminin was found to form distinct complexes with type IV collagen: one site of interaction is located 140 nm from the COOH-terminal, noncollagenous (NC1) domain and the other is located within the NH2-terminal region. The isolated NC1 fragment of type IV collagen does not appear to interact with laminin, while pepsin-treated type IV collagen, which lacks the NC1 domain, retains its ability to form complexes with laminin. Analysis of the laminin-type IV complexes indicates that laminin binds to type IV collagen via the globular regions of either of its four arms. This finding is supported by experiments using fragment P1 of laminin which lacks the globular regions and which does not bind to type IV collagen in a specific way. In addition, after heat-denaturation of laminin no specific binding is observed.