Blood anticoagulated with CPD was mixed with lactated Ringer's solution, 5 per cent aqueous dextrose, 5 per cent dextrose in 0.225 per cent saline, 5 per cent dextrose in 0.9 per cent saline, and 0.9 per cent saline solution in varying concentrations and incubated at room temperature and 37 C. Clots formed in the blood-lactated Ringer's mixture after five minutes at a citrate:calcium molar ratio of 4:1 or lower. Aqueous dextrose-blood mixtures showed immediate clumping with gross hemolysis after 30 minutes incubation. Blood mixed with 5 per cent dextrose and 0.225 per cent saline hemolyzed within ten minutes incubation at 37 C. No hemolysis occurred in blood mixed with 5 per cent dextrose in 0.9 per cent saline or with 0.9 per cent saline. Traces of solutions labeled with Evans blue dye remained in intravenous administration tubing even 30 minutes after a simulated transfusion was begun. Lactated Ringer's solution and 5 per cent dextrose in 0.225 per cent saline should not be administered concurrently with blood. Lactated Ringer's solution may also be harmful when used to start transfusions as it rapidly produces clots when mixed with CPD blood.