The antibiotic resistance pattern, the plasmid content and the auxotypes of 27 PPNG and 200 non-PPNG isolates obtained in 1984-1985 were examined. The well-known plasmid patterns, the most frequent was the combination of 4.5 and well-known plasmid patterns, the most frequent was the combination of 4.5 and 2.6 Mdal plasmids. The strains with the Asian-type (4.5 Mdal) plasmid belonged to the auxotypes Pro and Zero, whereas those with the African type (3.2 Mdal) plasmid were of auxotypes Zero, Arg and Pro, Arg. All PPNG strains exhibited reduced sensitivity at least to one of the other antibiotics tested (cefotaxime, spectinomycin, thiamphenicol, tetracycline). Among non-PPNG strains, 19% harboured the conjugative and the cryptic plasmid, 67.5% only the cryptic, 1% only the conjugative and 12% were plasmid-free. The most frequent auxotypes of non-PPNG strains were Zero (65.5%) and Pro (21%), while the uncommon auxotype Pro, Arg degree, Ura was found only in plasmid-free strains with reduced sensitivity to penicillin. Susceptibility testing revealed a large number of non-PPNG strains with decreased sensitivity to antibiotics, the Pro and Zero isolates being less sensitive than those of other auxotypes.