A porous balloon or other catheter structure is formed by creating specific size pores for delivering an agent to a body lumen. The pores can be created by passing matter or energy through the surface of the catheter structure, as by a laser or a projectile. In the case of a laser, the catheter structure can be reversed so that the inner surface becomes the outer surface to convert diverging pores into converging pores. In the case of projectiles, a pore size can be achieved by selecting an appropriate size and shaped projectile to obtain the desired characteristic. Alternatively, a material to make the catheter structure can include impurities that can be removed once the catheter structure is set, leaving pores where the material formed around the impurities.