Hi Ellen and welcome! I use BD U-100 syringes with half unit markings. When my Ruby was first diagnosed, the vet gave us prescriptions for her insulin and her syringes and so I got them both at the local pharmacy. The next time I ordered then on Amazon where I didn't need a prescription, and then finally I found the best deal on ADWdiabetes.com, who require a prescription but they will call your doctor and their customer service is excellent. Hope this helps!