A three-dimensional (3D) printing method includes applying a build material, including: a plurality of first reactive particles; a plurality of second reactive particles, the first and second reactive particles to react with each other upon contact there with; and a coating on i) the plurality of first reactive particles; or ii) the plurality of second reactive particles; or iii) both i) and ii). The coating is to isolate the plurality of first reactive from the plurality of second reactive particles. A fluid is selectively applied on a portion of the build material, the fluid disrupting the coating on the portion of the build material to render the first and second reactive particles in the portion of the build material in contact with each other. The contact initiates mutual reacting and fusing between the first and second reactive particles.