The average concentration in 75 female/male patients was 1.90 +/- 1.10/1.55 +/- 0.62 mg/l in serum, 0.81 +/- 0.42/0.74 +/- 0.48 mg/kg in bone, 2.40 +/- 1.16/1.94 +/- 0.87 mg/kg in cartilage, and 2.35 +/- 1.28/1.99 +/- 1.02 mg/kg in mucosa. In each case the highest serum or tissue concentrations were observed 2 hours after the last ofloxacin administration (serum 2.60 +/- 0.41 mg/l, bone 1.10 +/- 0.75 mg/kg, cartilage 3.40 +/- 0.86 mg/kg, mucosa 3.50 +/- 1.05 mg/kg), but even 8 hours after the last dose the levels still exceeded the MIC 90% of e.g. Pseudomonas aeruginosa, Staphylococcus aureus or Haemophilus influenzae. The clinical investigations carried out show that ofloxacin represents a new oral therapeutic agent of significant value in otorhinolaryngology, particularly in the treatment of problematic infections. As the investigations show, the level in healthy tissue is definitely within the therapeutic region for a period of 8 hours. In ENT (nasal and paranasal) infections, ofloxacin should be given for defined indications, e.g. for oral therapy of problematic infections due to P. aeruginosa, and if possible after identification of the pathogen.