The efficacy of two chalcogenoxanthylium photosensitizers to reduce pathogens in red cell suspensions while maintaining red cell storage properties was investigated in the presence and absence of the red cell band-3 ligand and antioxidant, dipyridamole (DP). In the presence of DP, both sensitizers, TMR-S and DJD-42, displayed potent virucidal photoactivity (>6 log₁₀) and species-dependent bactericidal activities that ranged from 0.6 to 8.7 log₁₀. Addition of DP to red cell suspensions containing TMR-S or DJD-42 reduced Day 42 photoinduced hemolysis by approximately eight-fold and four-fold, respectively. Red cell binding studies revealed only a small degree of competition between DP and TMR-S, and no competition between DP with DJD-42 for binding to red cell membranes, suggesting that protection of red cells by DP in this system may primarily stem from its antioxidant properties.