3 patients with mycobacterial lung infections, one due to Mycobacterium avium-intracellulare and 2 due to M. tuberculosis, developed ciprofloxacin-induced acute renal dysfunction while receiving the drug together with other antimycobacterial agents. These episodes took place 8-10 days after commencement of therapy and recovered spontaneously after cessation of all antimycobacterial drugs for 2-8 weeks. No recurrence was noted when patients were restarted on regimens that did not contain ciprofloxacin.