Objective[|]Aspirin intake of specific daily doses are advised by doctors to postmenapausal women and men above 40 years of age to prevent heart attack and even cancer in recent times. In vitro cytototoxic effects of different doses of ethanol (50 mM, 100 mM ve 200 mM) alone and together with 100 μg/mL aspirin, and possible protective role of 1 mM betaine on rat brain synaptosomes were investigated.[¤]Materials and Methods[|]Fifteen male Sprague Dawley rat forebrains were divided into equal pieces and pooled to form ten study groups. Synaptosomal fractions extracted from pooled rat brains were incubated with different doses of ethanol, aspirin and betaine, and malondialdehyde (MDA) levels, an important indicator of cellular damage, were measured.[¤]Results[|]A significant increase (p<0.05) was observed in MDA level of 200 mM ethanol group compared to control group. Different doses of ethanol (50 mM, 100 mM ve 200 mM) + aspirin exposure significantly increased (p<0.001) MDA levels compared to controls, whereas betaine administration significantly decreased (p<0.001) lipid peroxidation caused by ethanol+aspirin treatment.[¤]Conclusion[|]We conclude that ethanol and ethanol+aspirin administration increases lipid peroxidation in rat brain synaptosomes while betaine helps prevent this peroxidative membrane injury.[¤]