The role of theophylline in weaning infants weighing less than 1,250 g at birth from mechanical ventilation was evaluated. Infants were randomized into control or theophylline treatment groups when they required minimal ventilatory support (peak inspiratory pressure 12 cm H2O, positive end-expiratory pressure 2 cm H2O, rate 12 breaths per minute, and FiO2 less than 0.3), and they were extubated 24 hours later. Infants required reintubation if they had (1) PaCO2 greater than 55 mm Hg and pH less than 7.20, (2) FiO2 greater than 0.5, or (3) apnea associated with a heart rate less than 100 beats per minute that required frequent stimulation (more than 20 episodes during a 16-hour period). Among 32 infants (birth weight less than 1,000 g) who reached minimal ventilatory support before seven days after delivery, 13 of 18 (72%) control infants required reintubation, whereas only four of 14 (28%) theophylline-treated infants required reintubation. On the other hand, among infants (birth weight less than 1,000 g) who reached minimal ventilatory support after seven days following delivery, only one of six (17%) of the control group required reintubation and no improvement could be seen with theophylline treatment. Similarly, among control infants (birth weight 1,001 to 1,250 g), only ten of 45 (23%) required reintubation after reaching low intermittent manditory ventilation settings. In summary, most infants recovering from respiratory distress syndrome who had birth weights (1) greater than 1,000 g or (2) less than 1,000 g and who were older than seven days could be successfully extubated from minimal ventilatory support without theophylline treatment.(ABSTRACT TRUNCATED AT 250 WORDS)