To determine the role of dietary cholesterol on malondialdehyde (MDA) modification of proteins, the cerebral microvessels of rabbits fed a cholesterol enriched diet for 8 weeks were compared to control rabbits. The MDA proteins were estimated with immunoblotting using a specific polyclonal antiserum against MDA proteins. Cholesterol-fed rabbits had a significantly increased MDA protein band at 175 kDa compared to control rabbits (65.6 ± 6.8 OD versus 16.5 ± 2.5 OD, P < 0.01). An increase in MDA protein was also found in rabbits intravenously injected with 2 mg of MDA-modified low density lipoproteins or MDA-modified rabbit serum albumin (RSA) at 0, 2, and 4 weeks of observation. The MDA proteins were not increased in cerebral tissue of cholesterol-fed rabbits. It is concluded that a high cholesterol diet is associated with increased MDA modification of proteins in cerebral microvessels. The mechanism could be related to increased circulatory MDA proteins since exogenously administered MDA-LDL or MDA-RSA resulted in similar increases in MDA proteins in cerebral microvessels.