Pseudomonas aeruginosa was transformed with pUC8: 16, a pUC-based plasmid bearing the gene (vgb) encoding Vitreoscilla ( bacterial) hemoglobin (VHb). Transformation was initially indicated by an increase in ampicillin resistance from 1500 to 2500 mg l(-1). Presence of the plasmid in P. aeruginosa was confirmed by amplification of a portion of vgb from and detection of VHb in the transformant but not the untransformed host. Southern blot analysis further indicated that pUC8: 16 existed as an autonomous plasmid rather than integrated into the chromosome of the P. aeruginosa transformant.