Several red cell storage properties were evaluated following phototreatment with methylene blue (MB) under conditions that inactivated > or = 6 log10 of added vesicular stomatitis virus. Red cell 2,3 DPG levels were similar to untreated controls throughout conventional 42-day storage at 4 degrees C. Plasma hemoglobin levels were elevated approximately twofold in MB-phototreated samples, and morphology scores were 5 percent lower after 42-day storage. ATP levels declined 30 percent in phototreated samples and in a control sample containing MB and not exposed to light. Lipid peroxidation was not observed in treated or control cells, nor were differences observed in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of ghost membranes derived from phototreated and control samples. Phototreated cells exhibited enhanced ion permeability; sodium and potassium levels approached equilibrium with the suspending medium within 4 to 7 days after treatment. Direct agglutination tests using rabbit anti-human IgG or rabbit anti-human serum albumin on MB-phototreated cells indicated that serum proteins had absorbed to the surface of treated red cells. Plasma depletion by washing red cells prior to phototreatment did not prevent protein binding upon subsequent addition of untreated autologous or group AB plasma. To a much smaller extent, phototreatment of plasma resulted in IgG association with untreated red cells. The addition of glutathione to red cell suspensions prevented IgG binding to phototreated red cells but did not prevent enhanced ion permeability. Taken together, these data suggest that the red cell surface is altered by virucidal MB phototreatment of vesicular stomatitis virus.