A membranoproliferative glomerulonephritis (MPGN) was diagnosed in 10 Yorkshire piglets, aged between 33 and 73 days, that had been submitted for routine autopsy. Matings of animals related to these piglets subsequently produced 15 offspring that had a membranoproliferative glomerulonephritis when examined at between 5 and 48 days of age. The principal light microscopic changes in all examined glomeruli of all affected piglets were thickening of the glomerular capillary walls and a conspicuous mesangial cell proliferation. The glomerular capillary walls of the affected piglets possessed a weak but distinct autofluorescence when stained with thioflavine T and a strong reactivity for complement factor 3 as demonstrated with immunohistochemical techniques. Ultrastructural examination revealed intramembranous dense deposits in the glomerular basement membranes of kidneys from all affected piglets. On the basis of the initial matings and the morphological observations, it is concluded that the described MPGN in Yorkshire piglets represents an inherited renal disease that is comparable to human MPGN type II-dense deposit disease.