Endophytic fungi produce a great variety of secondary metabolites both in vivo and in vitro. In this study, we characterized the ability of a sterile-mycelium endophytic fungus isolated from Espeletia sp. to control the growth of Phytophthora infestans in Petri dishes. Sequence from the ITS regions (internal transcribed spacer) of the endophyte showed 94% similarity to Diaporthe phaseolorum's. The antagonistic interaction between Diaporthe sp. and P. infestans was evaluated in three different culture media. Diaporthe sp. showed an antagonistic effect towards P. infestans, with some variation depending on which medium was used. In an attempt to identify possible genes involved in this antagonism, we detected a gene from the endophyte encoding an amylase, which was differentially expressed during this biotic interaction.