Dense-deposits disease is characterized by an original morphological aspect of the renal basement membranes which have an electron-dense appearance. The immunofluorescence studies showed C3 alone in kidney. Low serum C3 levels and the presence of C3 NF activity have been detected in this disease, demonstrating an activation of the complement alternative pathway. The observation of recurrence in transplanted kidneys contributed to establish the sequence of the morphological events and showed the dissociation between the serological complement profiles and the lesions. Although the nature of the dense deposits remains still unknown, the altered membranes are recognized by at least some anti-GBM antibodies.