A retrospective study of blood samples from 95 osprey (Pandion haliaetus) nestlings from Scotland and England, collected opportunistically over a 10-yr period, was performed to determine hematologic and plasma biochemistry reference intervals. The age of the sampled nestlings was estimated to be between 4 and 8 wk. Ninety-five percent reference intervals were determined for all hematologic and biochemical variables using parametric and nonparametric methods as appropriate. No blood parasites were detected. This is the first published study providing baseline reference data for osprey nestlings, and it is hoped the data will be of use to wildlife veterinarians and biologists in assessing the health of this species.