The study compared the effect of transporting blood samples by pneumatic tube (PT) and bicycle courier (BC) on platelet aggregation in 96 participants (43 women, 53 men). Platelet function was assessed by light transmission aggregometry with ADP agonists, arachidonic acid, ristocetin, collagen and epinephrine. BC transport resulted in a small but statistically significant reduction in aggregation versus PT: ADP (-2.5%, p=0.02), arachidonic acid (p=0.006), ristocetin (-2.0%, p=0.003), collagen (-3.0%, p=0.002), epinephrine unaffected (p=0.58). The reductions were more pronounced in women and diabetics, especially in collagen (up to -3.5%, p=0.02). Women had overall higher aggregation, e.g. to arachidonic acid (p=0.02). Antiplatelet drugs inhibited ADP, arachidonic acid, and epinephrine, but not collagen or ristocetin. PT transport caused a smaller increase in aggregation than BC, which is not clinically relevant for most patients, but may affect the results in subgroups with high platelet reactivity, women and diabetics.