Aims: To study the effect of oral administration of a quinolone on emergence of resistance in an indicator bacterial species from faecal flora. Methods and Results: Quinolone resistance was studied in Escherichia coli obtained from the faecal contents of pigs housed in nine commercial farrow-to-finish herds in France after administration of flumequine to sows. The percentage of quinolone-resistant E. coli increased in the faeces of sows after administration of flumequine ( mean 21(.)78% at day 7 vs 6(.)42% before treatment for nalidixic acid) and then decreased ( mean 12 6 and 10 4 at days 30 and 60, respectively for nalidixic acid), being not significantly different from initial values 1 month post-treatment. In young pigs, the proportion of resistant strains was lower and decreased over rearing period. Moreover, changes over time of both total E. coli and the proportion of resistant bacteria exhibited great inter-individual variability. Conclusions: Restoration of susceptible faecal flora occurred within 2 months after flumequine treatment. Significance and Impact of the Study: Effect of flumequine treatment of sows on the quinolone resistance of faecal E. coli of both sows and their progeny is noticeable but transitory.