ApoE3 dimers are present in human hippocampus. The presence of disulphide-linked dimers of apoE were detected by analysing samples under both non-reducing "NR" and reducing "R" SDS-PAGE conditions. The susceptibility of dimers to thrombin cleavage was tested using three different conditions; storage at -80°C with no enzyme added "No enz", incubation at 37°C in the presence of thrombin "Thr" or heat-inactivated thrombin "hi-Thr". TBS-soluble fractions from control apoE3 (A), AD apoE3 (B) and AD apoE4 (C) homozygous hippocampal tissue samples were analysed. Western blotting was performed using goat anti-apoE polyclonal antibody. The human brain samples (Con n = 1, AD n = 2) are identified according to the Case # code given in Table 1.