Summary. Studies were carried out to examine whether a single additive solution could support both platelet and red cell storage. An ionically balanced electrolyte solution fortified with citrate, glucose and bicarbonate was used. This solution has previously been shown to provide good platelet viability with storage for up to 7 d. Optimization studies demonstrated that with adenine added to this solution (CSM), it also allowed for satisfactory preservation of in vitro red cell parameters for up to 49 d of storage. Confirmatory paired in vivo post-transfusion studies were carried out in which platelets and red cells obtained from the same donor were processed and stored in CSM on one occasion, and in CPD-plasma (platelets) and AS-1 (red cells) on another occasion. Five paired studies were conducted with platelets stored for 5 d and red cells for 42 d; another five paired studies with platelets stored for 7 d and red cells for 49 d. Except for a slight decrease in platelet survival (P<0.05) with storage in CSM, there were no statistically significant differences in post-transfusion recoveries and survivals between test and control media, demonstrating that both platelets and red cells may be satisfactorily stored in a combined single additive solution.