Agonist-induced platelet aggregation in PRP prepared from normal (N) or patient (P) blood. Platelet aggregation was measured in an aggregometer (dual channel from Chrono-Log) and aggregation was indicated by an increase in light transmittance. Aggregation responses to ADP (10 μM), collagen (2 μg/mL), PMA (100 nM), and adrenaline (5 μM) were examined. The tracings shown are from an experiment representative of 3 others with essentially similar results. Arrows indicate points of agonist addition.