Background. The compensatory increase in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) which follows a reduction in renal mass may be mediated by growth hormone, a renal vasodilator. Methods. GFR, ERPF and glomerular morphometry were assessed in the dwarf rat, selectively deficient in GH, and compared its Lewis base strain. Studies were performed 21-days after sham-operation, unilateral nephrectomy or subtotal nephrectomy in age-matched animals. GFR and ERPF were assessed from the renal clearance of inulin and p-aminohippurate measured under barbiturate anaesthesia. Results. The dwarf rat had a lower GFR and ERPF than the Lewis rat, in proportion to its lower body weight and lower kidney weight. Kidneys from the dwarf rat had a similar number of glomeruli to the Lewis, but smaller glomerular components in proportion to a lower kidney weight. Following unilateral nephrectomy, GFR (dwarf 58%,Lewis 53%) and ERPF (dwarf 58%,Lewis 52%) increased to a similar degree in both rat strains. Glomerular diameter, volume and capillary surface area increased in proportion to kidney growth, although compensatory renal growth (dwarf 62%,Lewis 78%) was somewhat lower in the dwarf. Following 5/6 subtotal nephrectomy, GFR (dwarf 143%,Lewis 171%) increased to a similar degree in both rat strains while ERPF (dwarf 108%,Lewis 48%) and compensatory renal growth (dwarf 115%,Lewis86%)weregreaterinthedwarfthantheLewisrat.Subtotalnephrectomywasalsoassociatedwithanincreaseinthethicknessoftheglomerularbasementmembraneinbothratstrains.Conclusions.TheresultsdonotsupportaroleforGHinthecompensatoryincreaseinrenalfunctionorhypertrophywhichfollowsareductioninrenalmass,excludingthisasapotentialmechanismforGH-dependentrenalscarring.