Oral ciprofloxacin was used at doses ranging from 500 mg to 1500 mg twice daily for 15 to 476 (mean 139) days for treatment of acute or chronic osteomyelitis in 38 patients, and acute arthritis in two. Clinical efficacy could be evaluated in 34 patients; 22 had resolution of their osteomyelitis, five improved and there were seven failures. Pseudomonas aeruginosa was the causative agent in 28 patients. It was eradicated in 22 patients, persisted but remained sensitive to ciprofloxacin in three and persisted with emergence of resistance to ciprofloxacin in three. Nineteen other pathogens, five Gram-negative and 14 Gram-positive, were isolated. Of those, one strain of Staphylococcus aureus, two of Staph. epidermidis and three of Streptococcus faecalis remained sensitive to ciprofloxacin during treatment. In one patient, Slr. faecalis persisted with emergence of resistance to ciprofloxacin. Ten adverse events related to ciprofloxacin treatment were observed in nine patients; two phototoxic reactions, two cases of impaired colour vision, and one each of exanthema, abdominal pain, malaise, drug fever, peripheral neuropathy and eosinophilia. In three patients the adverse events led to treatment discontinuation. In conclusion, ciprofloxacin seems to offer an oral alternative to injectible antibiotics in patients with osteomyelitis caused by Gram-negative bacteria, including Ps. aeruginosa.