Abstract: A process for the production of a chimeric antibody, comprising: a) preparing a replicable expression vector including a suitable promoter operably linked to a DNA sequence comprising a first part which encodes at least the variable region of the heavy or light chain of an Ig molecule and a second part which encodes at least part of a second protein; b) if necessary, preparing a replicable expression vector incuding a suitable promoter operably linked to a DNA sequence which encodes at least the variable region of a complementary light or heavy chain respectively of an Ig molecule; c) transforming an immortalized mammalian cell line with the or both prepared vectors; and d) culturing said transformed cell line to produce the chimeric antibody; chimeric antibodies produced by this process; and plasmids and transformed cell lines used in the process.