Introduction: Dobermann dogs are reportedly predisposed to familial glomerulonephropathy. Proteinuria is a hallmark of canine familial glomerular diseases. The identification of glomerular abnormalities in breeds so predisposed is of great importance in improving breeding policy. Therefore, markers that allow the detection and localisation of renal damage are needed. The purpose of this study was to investigate the urinary concentrations of immunoglobulin G (uIgG), retinol-binding protein (uRBP), and Tamm–Horsfall protein (uTHP) in a family of Dobermanns with proteinuria and compare these concentrations with the corresponding values in healthy controls. Material and Methods: Ten dogs of the Dobermann breed with proteinuria (five with a urine protein-to-creatinine ratio (UPC) of 0.5–1 and five with a UPC >1) and twelve healthy dogs were enrolled. An ELISA was performed to measure uIgG, uRBP, and uTHP, and these proteins were quantified in relation to urinary creatinine (uCrea). Results: uIgG/uCr and uRBP/uCr were significantly higher in the family of Dobermanns than in the healthy dogs. A significant difference in the uTHP/uCr value was found only in dogs with a UPC of >1. Conclusion: IgG seems to facilitate the diagnosis of primary hereditary glomerulopathy in Dobermanns. Moreover, in affected dogs, proteinuria characterisation seems to be a promising alternative option for the detection and localisation of renal lesions.