Abstract. The aim of this study was to compare the intensity of typical late complications in diabetic patients (n = 65, 28 type I, 37 type II) who were not on glycoside drugs with low vs. high serum levels of digoxin-like immunoreactive factor (DLIF: group I, n = 42, DLIF ≤ the detection limit of 0·2 ng ml−1; and group II, n = 23, mean ± SEM: 1·17 ± 0·31 [0·25–4·96] ng ml−1). For detection of nephropathy, urinary albumin excretion (24 h) and creatinine clearance tests were used. For coronary heart disease a questionnaire and standard ECG; for peripheral occlusive vascular disease a questionnaire; for eye disease a fundoscopy; for neuropathy a neurological score system; and for autonomic neuropathy a standardized test battery was employed. Patients with high DLIF levels showed better test results in vibratory perception (95·7 ± 1·5 vs. 82·8 ± 3·8%, normal finding = 100%, 2p = 0·016), had better percentile localizations concerning maximal pupillary area in darkness (28·4 ± 6·6 vs. 8·1 ± 1·8%, 2p = 0·0004), contraction velocity at 1 s (21·5 ± 5·8 vs. 8·0 ± 2·2%, 2p = 0·012), and dilation velocity at 6 s (23·0 ± 6·8 vs. 10·5 ± 2·5%, 2p = 0·041), had less retinopathy (with retinopathy: 26·1% vs. 64·3%, 2p = 0·0028), and better percentile localizations in the respiratory sinus arrhythmia test (68·4 ± 7·3 vs. 44·1 ± 4·9%, 2p = 0·0064). There was no difference concerning nephropathy, blood pressure, coronary heart disease and peripheral vascular disease. Separate analysis according to the type of diabetes confirmed the results in each group. This would indicate that DLIF is a possible protective endogenous substance for eye disease, and peripheral (large sensory fibres) and autonomic neuropathy in diabetic subjects independent of the type of diabetes.