Human blood platelets are stored in blood banks for 5 days, after which they are discarded, by federal regulation. This short lifetime has led to a chronic shortage of platelets, a problem that is particularly acute in immunosuppressed patients, such as those with AIDS. We report here that platelets can be preserved by freeze-drying them with trehalose, a sugar found at high concentrations in organisms that naturally survive drying. We suggest that these findings will obviate the storage problem with platelets. Trehalose is rapidly taken up by human platelets at 37 degrees C, with loading efficiencies of 50% or greater. Fluid-phase endocytosis plays an important role in this efficient uptake of trehalose, but other mechanisms may also be involved. Trehalose-loaded platelets were successfully freeze-dried, with excellent recovery of intact platelets. Rehydration from the vapor phase led to a survival rate of 85%. The response of these platelets to the agonists thrombin (1 U/ml), collagen (2 microg/ml), ADP (20 micromM), and ristocetin (1.6 mg/ml) was almost identical to that of fresh, control platelets. Analysis by Fourier transform infrared spectroscopy demonstrated that the membrane and protein components of trehalose-loaded platelets after freeze-drying, prehydration, and rehydration were remarkably similar to those of fresh platelets.