Twenty strains of filamentous fungi were tested for their ability to grow on a liquid medium containing caffeine (1,3,7-trimethylxanthine) as a sole nitrogen source. Seven strains which were able to grow on caffeine belong to the Aspergillus and Penicillium genuses. They all presented the snr?le degradation pathways but varied in the efficiency by which degradation took place. Caffeine was first demethylated in position 7; this lead to the formation of theophylline (1,3-dimethylxanthine). This compound was next demethylated in position I to give 3-methylxanthine. All these strains were also able to grow on theophylline, theobromine (3,7-dimethylxanthine), and paraxanthine (1,7-dimethylxanthine) as a sole nitrogen source. All degradation intermediates detected were methylxanthines.