The safety, acceptability and efficacy of nedocromil sodium, given by metered dose inhaler at a dosage of 4 mg four times daily, were investigated in a 52-week open assessment study of 79 perennial bronchial asthmatic patients maintained on oral bronchodilator therapy. Extensive laboratory monitoring of renal, hepatic and haematological functions before, during and at the end of the study failed to provide any evidence of drug-induced toxic effects. Nedocromil sodium was well tolerated with no serious adverse effects reported. Nineteen patients were withdrawn from the study, two complaining of sore throats and one of severe cough after nearly 1 year of treatment. The remainder were withdrawn because of intolerance to theophylline (one patient), non-cooperation (three), relocation outside the trial area (seven), onset of uncontrolled asthma (two) and pregnancy (three patients). Although this was an open assessment study, analysis of the diary card measurements and clinic assessments indicated that nedocromil sodium is an effective long-term therapy in the maintenance treatment of bronchial asthma.