Abstract: Systems for delivering a therapeutic agent to a selected site in a subject are disclosed. These systems enable precise placement of selected amounts, e.g., very small amounts, of a therapeutic agent to a predetermined site or sites in a three dimensional array in a subject with minimal trauma to the subject. These delivery systems include a guide cannula for penetrating a selected site in a subject to a predetermined depth and a delivery cannula for delivering the therapeutic agent to the subject. The guide cannula has an axial bore extending therethrough with an open proximal end and an opening at a distal portion thereof. The delivery cannula has an axial bore extending therethrough, a flexible distal end portion, and an outer diameter which is less than the inner diameter of the guide cannula. Methods of delivering therapeutic agents to selected sites in a subject using these delivery systems are also described.