Syntaxin 2 and syntaxin 4 are present in platelets. SDS-PAGE and Western blotting analyses were employed to determine if previously identified syntaxins are expressed in platelets. Total homogenates (HPH) and membrane extracts (HPE) from platelets were separated by SDS-PAGE and then electroblotted onto nitrocellulose. These blots were probed with the specific antibodies HPC-1 (syntaxin 1a,b), antisyntaxin 2 (syntaxin 2), antisyntaxin 3 (syntaxin 3), antisyntaxin 4 (syntaxin 4), and antisyntaxin 5 (syntaxin 5). The following samples (Control) were used as positive controls for the specific antisera: HPC-1, detergent-solubilized bovine brain membrane extract (BBE, 0.5 μg); antisyntaxin 2, recombinant syntaxin 2 (2.5 ng); antisyntaxin 3, recombinant syntaxin 3 (5 ng); antisyntaxin 4, recombinant syntaxin 4, (2.5 ng); antisyntaxin 5, HepG2 cell detergent-solubilized membrane extract (200 μg).