It is widely believed that theophylline is a valuable addition to beta-agonists in the treatment of asthma. This is true when beta-agonists are given in low doses, but available evidence suggests that theophylline adds little or nothing to the effect of maximal doses of beta-agonists. Clinical trials, albeit some with limitations, in acute asthma support the view that theophylline confers no benefit on patients treated with high-dose beta-agonists. As theophylline is a difficult drug to use safely, and its toxicity is serious, its use should be confined to unusual circumstances, and the dose should be small.