• The purpose of our prospective randomized study was to compare the efficacy of theophylline ethylenediamine and caffeine sodium citrate in the treatment of idiopathic apnea in premature infants. Sixteen infants with three or more severe apneic attacks were studied. Twenty-four-hour cardiorespiratory recordings immediately before and after randomization and four days later showed similar significant decreases of the apnea frequency in both theophylline- (group 1, n=8) and caffeine-treated infants (group 2, n=8). No undesirable side effects were observed, except for tachycardia in one infant in group 1. We suggest reasons for preferring caffeine to theophylline in the control of idiopathic apnea in premature infants: caffeine is as efficient and easier to administer.