Abstract: Ultrasound-guided rete testis injection/aspiration devices and methods are described. Some methods include inserting a needle into the rete testis space of a patient and injecting a therapeutic medium through the needle into the rete testis space and seminiferous tubules of the testis. The therapeutic medium can help to treat infertility. In some examples, the method can include monitoring intra-testicular pressure of the patient. In some examples, the therapeutic medium can include stem cells. In some examples, the therapeutic medium can include gene therapy vectors. In some examples, the method can include flushing the rete testis space and seminiferous tubules with a saline solution through the needle. Exemplary devices can include a dual lumen needle, a collection tube, a dual function pump, and flexible tubing. The dual function pump can include a dual syringe pump and a vacuum pump.