All of five lyophilised cultures of Mycoplasma orale kept for 23 years at room temperature were still viable, as were all but one of 12 lyophilised cultures of six Mycoplasma spp. that had been stored for 18-22 years at 4 degrees C. Similarly, 11 of 13 lyophilised ureaplasma cultures were viable after 8-22 years at 4 degrees C; the titre of organisms in the viable cultures had diminished no more than 100-fold. Seven broth cultures of five different Mycoplasma spp. all proved viable 5-13 years after being frozen and stored at -70 degrees C, although there was up to 10(4)-fold reduction in the titre of organisms in some cultures. Furthermore, 18 (82%) of 22 different Mycoplasma spp., originally lyophilised and then reconstituted and stored at -70 degrees C, were viable after 16 years. Viable organisms were found, with little or no reduction in titre, in all of seven broth cultures of Ureaplasma urealyticum, comprising six serotypes, after storage for 6-10 years at -70 degrees C, but five of 18 broth cultures of other human and animal ureaplasmas stored likewise were not viable after 13-14 years and in a further seven of them the titre of viable organisms had diminished greater than or equal to 10(4)-fold.