We have expressed in Escherichia coli cDNA corresponding to human lamins A and C, together with a number of fragments produced using site-specific mutagenesis. The proteins produced in this way were characterised both biochemically and ultrastructurally, and appeared to retain their native conformation. Crosslinking showed that all fragments formed 4-chain molecular dimers ('tetramers') analogous to those formed by intact intermediate filament proteins. Shadowed preparations showed the presence of rod-like particles that closely resembled those observed for other intermediate filament proteins and their proteolytically prepared rod domains. Moreover, the expressed lamins and a series of fragments in which different domains had been deleted formed paracrystals similar to those observed with native material. Deletion of either the N- or C-terminal non-helical domains altered the solubility and aggregation properties of the expressed protein, indicating that both domains have a role in lamin assembly.