Fragment EcoRI 7 from Ti-plasmid pTi Ach5, a part of the T-DNA in octo-pine tumors, was cloned in both orientations into pACYC184 and expressed in E.coli minicells. The cells synthesized four proteins from four different coding regions on EcoRI 7. Two of the proteins (M_r 25.000 and 26.000) were expressed with promoters from the Ti-plasmid fragment, while transcription for the two other proteins (M_r 18.000 and 74.000) started with a promoter on pACYCi84. The M 18.000 protein represented a fusion product between chlor-amphenicol acetyltransferase (CAT) on pACYC184 and a part of lysopine dehydrogenase (LpDH), the enzyme synthesizing octopine and lysopine in plant tumor cells. The results suggest that E.coli minicells are a valuable system to study the proteins coded for by the T-region of Ti-plasmids.