To determine if the membrane disordering effect of ethanol on cerebral microvessels is altered with age, the steady state fluorescence polarization (P) of diphenyl-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) which report on the membrane core and surface region, respectively, was determined in isolated cerebral microvessel membranes from 3-month-old (young) and 24-month-old (aged) male Fischer 344 rats in the absence or presence of 0, 25, 50, 100, 200, and 400 mM ethanol. The addition of ethanol resulted in concentration dependent decrease in DPH fluorescence polarization in both young and aged rat cerebral microvessels. Analysis of variance indicated that these two age groups did not differ from each other in their response to ethanol over this concentration range or in their baseline P. However, the TMA-DPH fluorescence polarization in cerebral microvessels in the absence or presence of various concentrations of ethanol was significantly lower in aged rats (p < 0.01). It is concluded that aging in rats is associated with a decreased membrane lipid order near the membrane surface of cerebral microvessels as assessed by TMA-DPH. Membrane disordering effect of ethanol on cerebral microvessels does not appear to be altered significantly with age.