Many patients with asthma often experience a deterioration of symptoms at night and in the early morning resulting in sleep disruption and possibly impaired daily performance. A bronchodilator agent which exerts its maximal effect overnight to control nocturnal symptoms, without a worsening of the disease during the daytime, should improve the treatment of asthma. In the case of theophylline, it has been shown in asthmatic patients that a chronotherapeutically optimized formulation which provides the highest serum theophylline concentrations during the critical early morning hours resulted in better airflow levels overnight than the conventional twice daily regimen without loss of airflow in the afternoon. During clinical routine, this chronotherapeutically optimized drug delivery can only be ensured if there is no food interaction. In particular, dose dumping must be excluded. One absolute prerequisite for this is the pH-independent drug release in vitro. In addition to a "state-of-the-art" biopharmaceutic formulation, an easy-to-use guidance for individualizing the theophylline dose should be provided. This in turn is only possible if the concentration/time profiles show good reproducibility between subjects, from day to day, and for different dose levels. Finally, batch-to-batch bioequivalence has to be ensured. It is shown that Euphylong satisfies all of the above requirements.