A double-blind, randomized trial was carried out in 48 children to assess the effects of inhaled ipratropium bromide, fenoterol or a combination of both drugs in treating their moderately severe acute asthma. Doses were adjusted according to the age of the patients and administered by nebulizer. Measurements of pulse rate and respiratory rate and assessment of the severity of symptoms were made at fixed intervals during the first 2 hours on treatment. Repeat nebulizations were given, if necessary, at 2-hourly intervals. The results suggested that fenoterol provided the most adequate treatment and there was no evidence to indicate that the addition of ipratropium produced any improved benefit.