Pitch canker disease, which affects pines and is caused by the fungus Fusarium circinatum, cannot be effectively controlled at present. Current restrictions on the use of chemicals and fungicides in forests are driving research into alternative methods of reducing the damage caused by the pathogen. Biological control with fungal endophytes is a promising and environmentally friendly strategy. In this study, 154 endophyte isolates were selected from a collection of 546 fungi tested in a preliminary confrontation assay. These isolates were then tested against F. circinatum in an in vitro antagonism exper- iment. Four different types of indicators (length of the central axis of the colony of the pathogen, the shape coefficient, percentage inhibition of radial growth and percentage inhibition zone) were used to detect and quantify the antagonistic activity directed towards the pathogen by the endophytes. The six isolates that showed the most promising results were inoculated in the field, together with the pathogen, into seedlings of Pinus radiata, P. sylvestris, P. pinaster, P. nigra and P. pinea, to test whether they could reduce the damage caused by F. circinatum. In total, 138 endophytes displayed antagonistic activity towards F. circinatum in the dual cultures of the in vitro experiment. In the field test, the endophytes Chaetomium aureum and Alternaria sp. reduced the area under disease progress curve (AUDPC) for the P. radiata seedlings, indicating that they may therefore be suitable for use as biological control agents (BCAs) of the disease.