Seventy-four pulmonologists and one allergist were recruited to assess the efficacy and safety of iodinated glycerol (Organidin), 60 mg qid, vs placebo in patients with stable chronic obstructive bronchitis in a randomized, double-blind, placebo-controlled, parallel design. A total of 361 patients (180 to iodinated glycerol and 181 to placebo) who complained of cough and difficulty bringing up sputum entered the eight-week study. Evaluations were based upon eight primary symptom efficacy parameters (cough frequency, cough severity, chest discomfort, dyspnea, ease in bringing up sputum, patient and physician global assessments, and a derived patients' global assessment), and six secondary parameters (frequency of aerosol bronchodilator use, incidence and duration of acute exacerbations, frequency of concomitant medication use, incidences of adverse experiences and dropouts). Cough frequency, cough severity, chest discomfort, patients' ease in bringing up sputum, patients' overall condition, and a derived subject global assessment were significantly (p less than 0.05) improved by iodinated glycerol as compared with placebo within eight weeks of treatment. Dyspnea showed a trend toward improvement and the physicians' global evaluation showed no significant difference between groups. Similar findings were noted in a subgroup analysis of moderately-to-severely affected patients. The mean duration (days) of acute exacerbations and number of dropouts attributable to adverse experiences were significantly less (p less than 0.05) in the iodinated glycerol group.(ABSTRACT TRUNCATED AT 250 WORDS)