Cytoskeleton models were produced by treating cultured human embryonal fibroblasts with Triton X-100 and actomyosin dissociating buffers. Morphological studies indicated that in addition to nuclear residues and intermediate filaments, both plasma membrane remnants and substratum-associated, pericellular material remained on the culture substratum. By immunochemical analysis the extracellular material was identified as fibronectin. The results suggest that fibronectin is associated with the nucleus-anchoring cytoskeleton of cultured human fibroblasts.