Support for a role of C3 in retinopathy and neuropathy is provided by data indicating that activated C3 and TCC/MAC (representing terminal pathway activation) are present in the retinal vessels [16] and choriocapillaries [17] of patients with diabetic retinopathy and in the walls of endoneurial microvessels of patients with diabetic neuropathy [18]. The gene discussed is C3; the disease is diabetic neuropathy.