Rings or arcs of fungus-stimulated plant growth occur often on the floor of woodlands which are commonly called "fairy rings". The fairy-ring forming fungi cause circles of mushrooms, rings or arcs of dark green grass due to luxuriant growth, or rings of dead grass. The liquid-cultured fungus was filtered, the filtrate was fractionated by successive chromatography, and the fractions were tested for their growth regulating activity on bentgrass. This lead to the purification of the active principles, 2-azahypoxanthine (AHX) and imidazole-4-carboxamide (ICA). Both AHX and ICA increased rice seed yield by 25.5% and 26.0%, respectively, in a greenhouse experiment. The growth-promoting activity of AHX was investigated using a rice oligo DNA microarray, reverse transcriptase-polymerase chain reaction, and bioassay. The results indicate that plants develop tolerance to various and continuous stress from the environment and increased nitrogen absorption by AHX-treatment, resulting in the growth promotion.