AbstractIn investigating the role of cell‐extracellular matrix interactions in cell adhesion and growth control, the effects of heparin on cell‐collagen interactions were examined. Exponentially growing Balb/c‐3T3 fibroblasts were radiolabelled with3H‐thymidine and detached from tissue culture surfaces using EDTA, and cell attachment to various types of collagen substrata was assayed in the presence or absence of heparin or other glycosaminoglycans (GAGs) or dextran sulfate (40 K). Cells attached readily (70–90%) to films of types I and V, but not to type III collagen. The number of cells bound to types I and V collagen films was inhibited by 10–50% when heparin was present from 0.1–100 μg/ml. Cell‐collagen attachment was also inhibited by dextran sulfate, and to a lesser extent by dermatan sulfate, but chondroitin sulfates A and C and hyaluronic acid showed no effect. Heparin was active even at early time points in the adhesion assay, suggesting it may disrupt cell‐collagen attachment. To study the effects of heparin in modulating cell growth on collagen, growth arrested cells cultured on type I collagen films were serum stimulated in the presence of heparin or other GAGs for 3 days. Growth was inhibited (>40%) only by heparin and dextran sulfate. Interaction of heparin fragments (Mr≤ 6KD) with type I collagen was analyzed by affinity co‐electrophoresis (Lee and Lander, 1991) and showed higher affinity heparin binding to native as compared with denatured collagen. These data suggest that sites within native collagen may mediate Balb cell–collagen and heparin‐collagen interactions, and such interactions may be relevant towards understanding heparin's antiproliferative act