High level tetracycline resistance of Neisseria gonorrhoeae is mediated by a 25.2-MD plasmid and is characterized by a minimal inhibitory concentration of 16 micrograms/ml or more. The 25.2-MD plasmid originated through the insertion of the streptococcal tetM determinant into the 24.5-MD transfer plasmid of N. gonorrhoeae. In the present study the prevalence of N. gonorrhoeae with high-level tetracycline resistance in the Heidelberg gonococcal population between 1981 and 1989 was determined. Among 1765 N. gonorrhoeae isolates, one strain with high-level tetracycline resistance was identified. The presence of the 25.2-MD plasmid in this strain was demonstrated by plasmid-agarose gel electrophoresis. The auxotype/serovar class proline-/IB-1 indicates the importation of this strain from the USA. The 25.2-MD recombinant plasmid, in contrast to the 24.5 MD transfer plasmid, has a rather wide host range, which is favourable to the occurrence both of high-level tetracycline resistance and of beta-lactamase plasmids in N. meningitidis.