Complementary DNA coding for human alpha 1-antitrypsin has been placed under the control of the lambda PR promotor carrier by the expression vector pCQV2 [1]. In conditions which allow transcription from this promotor (thermoinactivation of the repressor), Escherichia coli cells harbouring the recombinant plasmid pULB1114 express human alpha 1-antitrypsin (+/- 9000 molecules/cell). The product has a Mr of 44000, corresponding to mature unglycosylated alpha 1-antitrypsin.