Background and Objectives: Glycocalicin (GC) is a proteolytic fragment of GpIb and can conveniently be measured in supernatants of platelet concentrates (PCs) by means of a sandwich ELISA. Because of the convenience of the assay and easy sample storage, we tested its suitability as a sensitive platelet activation parameter during PC storage. Material and Methods: Filtered PCs in plasma or additive solution were made from 5 pooled buffy coats and were subsequently stored during 8 days at 22±2°C. Correlation coefficients (r) were calculated after comparison of GC levels with platelet parameters. Results: A significant increase in GC concentration was found on all subsequent sampling days. PC stored in plasma showed GC levels that correlated well with the soluble P–selectin levels (r = 0.7506), P–selectin (CD62P) expression on platelet membranes (r = 0.8843), morphology scores according to Kunicki (r = –0.7102), lactate concentrations (r = 0.9216), glucose concentrations (r = –0.8913) and β–thromboglobulin (β–TG) concentrations (r = 0.8913). In PCs stored in additive solution, the correlation coefficients with these markers were 0.9209 with soluble P–selectin, 0.7161 with CD62P expression, –0.7474 with morphology score, –0.8908 with glucose concentrations, 0.8923 with lactate concentrations and 0.8908 with β–TG concentrations. Conclusions: The GC concentration correlates well with sensitive platelet (activation) parameters, rendering it a sensitive and convenient parameter for platelet activation.