The Kedetm-Katchalsky equations and permeability data previously reported (F. G. Arnaud and D. E. Pegg. Permeation of glycerol and propane-1,2-diol into human platelets. Cryobiology 27, 130-136, 1990) have been used to design methods for adding and removing propane-1,2-diol (propylene glycol, PG) with human platelets. Mean platelet volume was kept within the tolerated range of 60 to 120% of normal. PG concentrations of 0.5, 1.0, 2.0, 2.5, and 3.0 M were studied at 2, 21, and 37 °C. PG was removed only at 21 °C. The effects of concentration of PG, temperature, and duration of exposure on the hypotonic stress response and ADP-induced aggregation were measured. It was found that platelets would tolerate exposure to PG concentrations up to 2 M at 21 or 2 °C for up to 15 min. The extent of damage increased considerably at higher temperatures and concentrations. These data provide the necessary basis for experiments to cryopreserve platelets with PG. © 1990.