An intravascular catheter for peri-vascular or peri-urethral tissue ablation includes multiple needles advanced through guide tubes which may be supported by an expandable balloon. The guide tubes expand with open ends around a central axis to engage the interior surface of the wall of the renal artery or other vessel of a human body allowing the injection an ablative fluid for ablating tissue, or nerve fibers in the outer layer or deep to the outer layer of the vessel, or in prostatic tissue. The diameter of the inflated balloon is less than the inside diameter of the vessel, allowing perfusion across the inflated balloon and guide tubes.