cDNA clones of the mRNA coding for tissue-type plasminogen activator (t-PA) have been obtained and their nucleotide sequences compared to those reported previously. A gene coding for t-PA has been reconstructed and inserted into vectors for expression in prokaryotic cells. Relatively high levels of t-PA accumulated in inclusion bodies in Escherichia coli containing an optimized expression plasmid, but only a small proportion of the insoluble protein was recovered as active enzyme using a variety of solubilization procedures.