Supernatant of aged PLTs have increased neutrophil priming capacity. Neutrophil priming activity of the aged PLTs expressed in pmol H₂O₂ release per minute per 10⁶ neutrophils. Supernatant of fresh PLTs (Day 0) showed an increased in vitro neutrophil priming capacity compared with buffer controls. Supernatant of aged PLTs stored for 2 days and 5 days showed an increased in vitro neutrophil priming capacity compared with supernatant of fresh PLTs. *P < .01. Data are presented as mean ± SEM.