End-stage kidney disease (ESKD) is a significant, expensive health problem that affects 4,500 New Zealanders and their families. Kidney transplantation improves survival, quality of life, and is much cheaper than dialysis treatment for ESKD. However sometimes kidney transplants function poorly after surgery, and a period of continued dialysis is needed. In addition to complicating recovery, this can adversely affect long-term kidney function and the health of the recipient. Intravenous fluids given during and after transplantation (usually sodium chloride, or saline) are critical to preserve kidney transplant function, but there is evidence that saline may not be the safest fluid to use due to its high chloride content. The BEST-Fluids study (Better Evidence for Selecting Transplant Fluids) is a randomised clinical trial in kidney transplantation comparing saline with a balanced low-chloride solution, Plasmalyte. The trial will determine whether using Plasmalyte will improve kidney transplant function, reduce complications and improve long-term outcomes.