An intravascular catheter for peri-vascular or peri-urethral tissue ablation includes multiple needles advanced through supported guide tubes which expand 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. A method can involve injection of the ablative fluid over an extended time period of at least 10 seconds or with two injections at two different penetration depths to reduce or eliminate patient pain during ablation.