The efficacy and tolerability of morniflumate suppositories used together with phenoxymethylpenicillin were studied in a placebo-controlled, double-blind trial in 101 children with acute tonsillitis. Patients received a suppository containing 400 mg morniflumate or placebo twice daily for 4 days; all patients also received 1,500,000 IU/day phenoxymethylpenicillin. Response to treatment was assessed by clinical examination before and after 2 and 4 days' treatment. Efficacy was evaluated by resolution of oropharyngeal pain, congestion, fever, size and sensitivity of adenopathies, quality of life and duration of sleep. Body temperature fell rapidly after the start of treatment. There was also resolution of pharyngeal pain, earache, dysphagia and adenopathy. Spontaneous pharyngeal pain was present after 4 days in significantly (P = 0.03) fewer patients receiving morniflumate than receiving placebo. It is suggested that morniflumate combined with antibiotic therapy is an effective and well-tolerated treatment for tonsillitis in children.