Ultrathin frozen sections of human platelets (a to f) immunolabeled with polyclonal antibodies against talin (a), caveolin (b), GP IIb (c), PF-4 (d), P-selectin (e), and PECAM-1 (f) using the 3-step labeling procedure. With the exception of caveolin, which is negative, each of these exhibits a unique labeling pattern that is unlike the clustered labeling pattern obtained with antibodies to the Src-related kinases seen in Fig 1a to d. Original magnification × 47,000.