Glomerular filtration rate (GFR) is a direct measurement of renal function. Although clearance tests using 24-h urine collection or blood sample series are gold standards for measuring GFR, serum-based prediction of GFR based upon the Modification of Diet in Renal Disease (MDRD) Study equation is acceptable for routine use in human adults. The purpose of our study was to assess the ability for a modified MDRD Study equation to predict expected changes in GFR in bottlenose dolphins (Tursiops truncatus) using a healthy dolphin population represented by 1,103 routine serum samples collected from 50 dolphins of all age groups, years 1998–2005. Predicted GFR was also calculated from serum collected from a 32-yr-old male dolphin with end-stage renal disease. The dolphin-adjusted MDRD equation predicted GFR changes in our population that paralleled what has previously been reported in other mammals, including decreasing predicted GFR with age (P < 0.01), higher predicted GFR in dolphins that had recently eaten (P < 0.01), and rapidly decreasing predicted GFR in the animal with end-stage renal disease. We conclude that a serum-based GFR prediction equation may be a feasible means of detecting and tracking renal function in bottlenose dolphins.