Crew members on deep space missions face the risk of acute radiation syndromes due to solar proton events (SPEs). Low gravity and ionizing radiation both produce transient anemia and immunodeficiencies, and are a concern for long term deep space missions. The C57Bl/6 based hindlimb-suspension model has been utilized to investigate the consequences of hindlimb suspension induced immune suppression on the sensitivity to whole body irradiations with high-energy protons. Eight week old C57Bl/6 female mice were put into hindlimb-suspension and serial tail bleeds and complete blood counts (CBCs) were performed weekly and compared to non-suspended controls. C57Bl/6 mice were also transported to the Medical Proton Radiotherapy Institute at the Indiana University Cyclotron Facility to determine LD20/30, LD50/30, and LD80/30. Successful hind-limb suspension up to 6 weeks has been achieved. Preliminary serial tail bleeds and CBC analysis of tail-suspended and control mice by HEMAVET indicate that one week of tail suspension reduced overall white blood cells counts by over 50% with the majority of that decrease due to 3 fold reduction in lymphocytes counts. These reductions were maintained for the entire six week period of observation. Neutrophil, RBC, and platelets counts were either not significantly or slightly reduced over the same interval. A preliminary proton irradiation with 6.5, 7.0, and 7.5 Gy of protons has recently been completed. Preliminary serial tail bleeds and CBC analysis of 7 Gy irradiated and control mice by HEMAVET demonstrate severe reductions in WBC counts (Lymphocytes and PMNs) by day 2 post-irradiation, followed a week to ten days later by reductions in platelets, and then reductions in RBCs about 2 weeks post-irradiation. Recovery of all blood components is underway three weeks post-irradiation. Our preliminary investigations are quite promising and indicate our approach will allow us to study the interaction of immune suppression and high-energy proton radiation sensitivity. Supported by Cooperative Agreement # NNJ06HE95A with NASA.