Five of six independent gonococcal isolates have been found to harbor a plasmid pool of covalently closed-circular deoxyribonucleic acid about 2.4 x 10(6) daltons in size. The plasmid species were 0.5-mol fraction of guanine plus cytosine and comprised 6 to 8% of the total gonococcal deoxyribonucleic acid equivalent, to approximately 24 to 32 copies per cell. There was no apparent correlation between the presence of these plasmid species and the in vitro clonal variation of gonococci associated with the loss of pili.