The intergenic spacer region between the 16S and 23S rRNA genes of Mycoplasma haemomuris, previously classified as `Haemobartonella muris', was amplified by PCR and sequenced for analysis of the primary and secondary structures of the RNA transcript. The spacer region consisted of 219 base-pairs and lacked the spacer tRNA gene. A hypothetical secondary structure predicted in the RNA transcript of the spacer region was tentatively assigned boxA and boxB loci peculiar to the members of the Mycoplasma. Mycoplasma haemomuris and the other species of the genus Mycoplasma are consistent with these characteristics of the spacer region.