The aim of our work was to evaluate tile sources of impaired nervous conduction in visual pathways in newly-diagnosed diabetic patients. We assessed Flash-ERG (ERG), oscillatory Potentials (OPs) and simultaneous recordings of Pattern-Electroretinograms (PERGs) and Visual Evoked Potentials (VEPs) in If! insulin-dependent diabetic patients (IDDM: aged 24.8+/-7.8 yrs, duration of disease 3.0+/-1.6 months) and in 14 age-matched control subjects. In IDDM patients we found: ERG and OP parameters similar to those in controls (ANOVA P>0.05), PERG and VEP latencies significantly (P<0.01) higher than in controls, a retino-cortical time(RCT) longer (P<0.01) than in controls. in IDDM patients, therefore, there are two sources ill the genesis of the functional impairment of VEP: one retinal (delayed PERG) and one postretinal (delayed RCT).