Gel filtered human platelets were mixed with polylysine coated polyacrylamide beads. Platelet binding to individual beads within one preparation was variable, yet high and the bound platelets appeared to involve non-activated platelets. Some cells appeared to be in contact with more than one bead. When the attachment process was neutralized with 1 mg/ml of polyanionic dextran sulfate, significantly fewer platelets remained attached to the beads. Platelets which were recovered in the washes also were non-activated. Attached cells were capable of being activated and underwent release reactions when exposed to either ADP or thrombin. Release reactions were monitored by the liberation of either serotonin or beta-thromboglobulin. Platelets which were iodinated prior to attachment gave evidence that the failure to neutralize the bead before vortexing resulted in lower specific activities of bound iodine/protein.