1974 to 1982 202 hospitalized patients, aged 17 to 87 years, suffering from a sudden hearing loss at first were treated between 3 and 26 days (average period 13 days) with 400 mg naftidrofuryl in low molecular weight dextrans, physiologic saline solution, glucose or leavulose solutions daily. After leaving hospital the patients received 2 dragees at 100 mg naftidrofuryl thrice a day. Provided that treatment starts within four days after the occurrence the average hearing loss measured by pure-tone audiometry was 49.2 dB before and 28.9 dB after treatment. After later beginning of therapy the values amounted to 50.8 and 35.5 dB respectively. 19 patients showed a complete remission and 77% of the patients an average hearing improvement of at least 10 dB over the measured frequencies.