Endothelial functional integrity was quantified in human saphenous vein by measurement of stimulated (vortex-mixing) rates of prostacyclin production. Prostacyclin production was not inhibited by dimethylsulphoxide (DMSO), glycerol or sucrose at concentrations normally used for cryopreservation. Rapid freezing followed by storage for 3-4 weeks and thawing of veins pretreated with 15% (v/v) dimethylsulphoxide significantly impaired prostacyclin production. In contrast, slow freezing and thawing in the presence, but not the absence, of DMSO led to complete retention of prostacyclin production. We conclude that endothelial function can be preserved during cryostorage.