Immuno-EM of wild-type platelets. Platelets from C3H/He^+/+ mice were processed for immuno-EM as described in Methods. Affinity-purified polyclonal anti-Rab27a Ab N688 was used to probe for Rab27a (a) and affinity-purified polyclonal anti-Rab27b S086 to probe for Rab27b (b). The labeling was found mainly in dense granules (arrowheads). Some labeling was also detected in α-granules (arrows). Bars, 100 nm.