Munc18b associates with syntaxin-11 and with other SNARE proteins. Extracts from resting or stimulated platelets were prepared with 2% n-octyl β-glucopyranoside for immunoprecipitation (IP) with rabbit anti-Munc18b antibodies (A) or 0.5% Triton-X100 for IP with rabbit anti–syntaxin-11 antibodies (B). IgG was used as a specificity control (A and B) and the immune-complexes were recovered with protein A-Sepharose beads. The bound complexes were then analyzed by Western blotting by the use of antibodies to the indicated proteins.