Nestifylline [ABC 99] is a methylxanthine derivative that was at the preclinical stage of development with ABC for the treatment of asthma. ABC 99 has been studied in the animal to evaluate its pharmacological activity. This compound was found to have antibronchospastic activity in vitro and in vivo markedly greater than aminophylline. The new compound also had moderate antitussic properties and was an active mucoregulator. ABC 99 acts as an intestinal muscle relaxant, but it has no cardiovascular, urinary, or CNS side effects. The mechanism of ABC 99 could be explained by its inhibition of guinea-pig lung phosphodiesterases and affinity for adenosine receptors, particularly A2 receptors. ABC 99 was observed to have marked anti-inflammatory activity in a series of experimental trials involving the principal mediators of inflammation (PAF, histamine, serotonin, LTC4-like substances, etc). ABC 99 is of particular interest in the treatment of respiratory disorders involving obstructive inflammation and bronchial hypersensitivity.