Mean platelet aggregation (± standard deviation) results from thrombocytopenic cord blood (CB) samples (gray bars) and adult peripheral blood (PB) samples (black bars) transfused in vitro with neonatal (CB) or adult (PB) platelets. Adult platelets aggregated better than neonatal platelets, regardless of the blood into which they were transfused, in response to thrombin receptor-activating peptide (TRAP), ADP, and collagen. The same trend was observed in response to ristocetin, but the differences were not significant. *P < 0.001, †P < 0.01, ‡P < 0.05. AUC, area under the curve; Plt, platelets.