It is known that nalidixic acid resistance is a relatively rare phenomenon among shigellae. Between June 1989 and May 1990, six strains of shigellae resistant to nalidixic acid were isolated. These strains also exhibited resistance to three newer fluoroquinolones, viz., ciprofloxacin, pefloxacin and enoxacin. In repeated experiments, nalidixic acid resistance did not transfer to a suitable recipient.