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Highly‐purified human fibronectin receptor (a heterodimer of two distinct subunits, alpha and beta) was studied using electron microscopy and a variety of preparative procedures. It was found that the receptor consists of a globular head approximately 80 by 120 A and two tails about 20 A thick and 180‐200 A long. The whole complex is approximately 280 A long. At low concentrations of detergent the receptor forms doublets, triplets or rosettes associated with the tails which possess the transmembrane portion of the molecule. Computer‐assisted structure prediction using the published amino acid sequence of both subunits showed differences in the secondary structure of the tails, the alpha‐tail being rich in beta‐strands, the beta‐tail having five cysteine‐rich repeats analogous to the EGF‐like repeats of laminin. Estimates of the length of the tails from the predicted structure conformed well with the dimensions obtained from electron micrographs.