Methods and compositions for producing secreted soluble receptors and biologically active polypeptides in trimeric forms are disclosed. The process involves fusing the DNA template encoding a soluble receptor with a ligand binding domain or biologically active polypeptide to a DNA sequence encoding a C-propeptide of collagen, which is capable of self-assembly into a covalently linked trimer. The resulting fusion proteins are secreted as trimeric soluble receptor analogs, which can be used for more efficient neutralization of the biological activities of their naturally occurring trimeric ligands.