Methods and systems infuse therapeutic materials into a vascular vessel by means of a catheter based infusion system. In especially preferred forms, the infusate (which comprises a therapeutic material) is infused through a distal end of the catheter and into the vascular vessel by delivering the infusate to the catheter at a substantially constant flow rate while simultaneously imparting a pressure amplitude and frequency to the infusate in dependence upon a sensed pressure condition within the vessel. Preferably, and the pressure amplitude imparted to the constant flow rate of infusate is about twice the vessel systolic pressure. The present invention is therefore especially well suited for the catheter-based infusion of relatively large particles, such as cellular, genetic, viral, polymeric or proteinaceous materials, intravascularly in dependence upon the pressure and flow characteristics of the infusate.