Children born prematurely frequently have recurrent respiratory symptoms at follow-up and benefit from bronchodilator therapy. We have assessed if regular inhaled sodium cromoglycate would reduce this respiratory morbidity and need for bronchodilator therapy. Sixteen symptomatic children (median gestational age 29 weeks, post-natal age 15 months) were entered into a randomized double-blind, placebo-controlled trial. In two 3-week periods, the patients received either placebo or sodium cromoglycate (5 mg) as one puff q.d.s. from an inhaler via a coffee cup. Parents recorded their child's symptoms and need for bronchodilator therapy throughout and lung function was assessed by measurement of functional residual capacity (FRC) at the beginning and end of each 3-week period. The symptom score was reduced by 49% in the active compared to the placebo period (P less than 0.01) and bronchodilator was taken on a mean of 2.9 days per infant in the active period compared to 7.9 days in the placebo period (P less than 0.01). There was a significant improvement in FRC in ten of 16 patients over the active period but only in two infants over the placebo period (P less than 0.01). We conclude regular inhaled sodium cromoglycate is useful prophylaxis for symptomatic pre-term children.