Abstract: Heterologous polypeptides are produced in lactococcus using a T7 or T7-like RNA polymerase gene under the control of an inducible promoter effective in a lactococcus host, and a promoter specific for said polymerase upstream of a coding sequence for the heterologous polypeptide. Thus, the promoter specific for the polymerase directs transcription of the coding sequence selectively as a result of expression of the polymerase. The heterologous polypeptide can be produced at high yield, and can be secreted. The polypeptide within the cell, being biologically active, can be delivered in the encapsulated form, e.g. as a medicament, vaccine or as an environmental pesticide.