We investigated the pathophysiological role of acetaldehyde protein adducts formed in vivo in organs of chronically alcohol fed male Wistar rats. Thirty male Wistar rats were fed on rodent pellets and 15% alcohol (V/V) for 5, 8 and 12 months, respectively before they were sacrificed. Further 30 male rats were chosen as the control group. We tested several organs by histological and immunohistochemical methods. Using immunohistological analysis, in the 12 months groups the basal membranes of glomerula, the membranes of liver, skeleton muscle and heart cells, and the gut were stained positively for acetaldehyde adducts. Using Western blotting of liver cell fractions (mitochondria/ lysosomes; microsomes; cytosol) adducts in charateristic molecular weight regions were detected. Approximately 30% of the sera of experimental rats contained antibodies against the acetaldehyde adducts formed in vivo. Immunologically detectable acetaldehyde adducts could be found in all rat organs tested. The stage of alcohol disease attained in this experiment after 12 months of ethanol feeding is described as the initial phase of manifestations of disturbances that are seen also in the carbohydrate metabolism.