Forty three strains of Neisseria gonorrhoeae with decreased sensitivity to quinolone antibiotics were detected amongst 2141 Australian isolates of gonococci examined in the years 1984 to 1990. The strains examined belonged to 23 different auxotype/serovar classes, were generally more resistant to other antibiotics and, in the majority of cases, were isolated from travellers entering or returning to Australia from SE Asia. Quinolone-sensitive wild-type gonococci became less sensitive to these agents in vitro at a relatively high frequency when grown in the presence of quinolone concentrations at or around the MIC (Mean Inhibitory Concentration) of the antibiotic. Further increments in the levels of quinolone resistance of the already less-sensitive gonococci were also produced by this means, but high-level resistance to these agents was not observed. This suggests that mechanisms other than alterations in the DNA-gyrase of the organisms were responsible for the changes seen. Although spread of quinolone resistance in gonococci in Australia is unlikely to be rapid, if these antibiotics are used in therapy, treatment regimens with higher rather than lower dosages of quinolone antibiotics should be employed.