An at least partly implantable system for injecting a substance into a patient's body, in particular a penis erection stimulation system comprises one or more infusion needles disposed within and implanted along with one or more housings adjacent the patient's left and right corpora cavemosa. A reservoir and a pump are also implanted inside the patient's body to supply the infusion needle with infusion liquid. A drive unit also adapted for implantation inside the patient's body is arranged for advancing and retracting the tip end of the infusion needle such that it penetrates the housing in at least one penetration area, preferably in two different penetration areas either simultaneously or in immediate time succession, thereby injecting drugs along with the infusion liquid into the patient's body for stimulating penis erection. The drive unit is provided for implantation remote from the injection area and comprises a mechanical drive element for transmitting kinetic energy from a remote location within the patient's body to the at least one infusion needle.
