DNA chromosomic sequences from Ureaplasma urealyticum were shown, by DNA hybridization, to possess homology with Providencia stuartii urease genes. The homologous ureaplasma DNA fragment was cloned in Escherichia coli and a DNA probe, designated IC61 probe was specific for only the urease-producing U. urealyticum among the Mollicutes. Genetic homology shown between the IC61 probe and urease genes from Campylobacter pylori, E. coli and P. stuartii suggests that (1) the cloned DNA fragment from U. urealyticum contains urease encoding sequences, and that (2) the urease genes possess conserved sequences among phylogenetically distant prokaryotes.