This invention is directed toward a process for reducing transfusion related complications in a recipient of an allogeneic blood transfusion by adding to the blood to be transfused a photosensitizer comprising riboflavin, irradiating the blood and riboflavin with light, transfusing the irradiated blood into a recipient, and reducing a transfusion related complication by the recipient to cells in the donor blood. The invention is also directed towards a process for preventing rejection of a donor organ by a recipient comprising the steps of transfusing the recipient of the donor organ with treated platelets; and transplanting the donor organ into the recipient.