The absorption profiles of Theolair-SR and Theo-Dur were studied in 23 asthmatic children (mean age 11 years). A 250-mg dose of each product was administered twice a day until steady state was attained (mean, 8 days). Both products maintained adequate theophylline levels over 12 hours, although Theolair-SR gave significantly higher serum levels and a 19% greater extent of theophylline absorption. The mean Cmax-Cmin was also significantly greater for Theolair-SR. Both products should be considered comparable for practical use.