A 23S ribosomal RNA gene of Pseudomonas cepacia has been cloned and sequenced. A general higher-order structure model based on earlier published models has been derived from comparative analysis of 23S-like rRNAs of eubacteria, archaebacteria, organelles and eukaryotes. Differences between the previous models were carefully analyzed and controversial regions evaluated. Moderately large insertions and deletions have been found at new points in the secondary structure. The analysis of 50 published as well as unpublished 23S rRNA sequences provide additional proof for six of the seven previously suggested tertiary interactions within the 23S rRNA. P. cepacia is the first representative of the beta subgroup of the Proteobacteria phylum whose 23S rRNA has been sequenced. A tree reflecting evolutionary relationships of prokaryotes was constructed. The topology of this tree is in good agreement with the 16S rRNA tree.