Acetaldehyde, the main metabolite of ethanol, is a highly reactive species that reacts with macromolecules to produce unstable and stable adducts. Acetaldehyde-modified proteins are immunogenic and have been detected in the liver and blood of alcoholics. Furthermore, antibodies reactive with acetaldehyde-modified proteins have been detected in the plasma of social drinkers and alcoholics. However, the class distribution of immunoglobulins reactive with modified proteins was different in the two groups, being predominantly immunoglobulin (Ig)M in social drinkers, but IgM and IgA in alcoholics. In this study, we demonstrate that heavy drinkers (alcohol intake > 130 g/week for females and 150 g/week for males) also exhibit IgA reactivity with acetaldehyde-modified proteins. The IgA adduct-specific reactivity (IgA reactivity with acetaldehyde-modified bovine serum albumin-reactivity with native bovine serum albumin) showed a moderate correlation with self-reported alcohol intake, but did not correlate with markers such as plasma transaminase, gamma-glutamyltransferase activity, or mean corpuscular volume. IgA adduct-specific reactivity had similar specificity to the conventional tests of alcohol abuse, but had higher sensitivity than the other tests, especially with heavy drinkers. Data presented herein demonstrate that elevated IgA reactivity with acetaldehyde-modified epitopes is associated with heavy drinking and is a potential marker for high alcohol intake.