Bovine longissimus muscle was excised from the right side of five market steers at 24 hours postmortem, and cut into 24, 1.9 cm strip loin steaks. These were randomized and placed into one of four treatment groups injected to a 10% weight basis at a final concentration with: (1) water, (2) sodium chloride/tripolyphosphate (0.75%/0.35%), (3) calcium chloride (0.15%), (4) sodium chloride/tripolyphosphate /calcium chloride (0.75%/0.35%/0.15%). Each of the four groups was post-mortem aged at 2°C for three, six, or thirteen days post-mortem. Sensory evaluation, Warner-Bratzler shear, water holding capacity (WHC), myofibril fragmentation index (MFI), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and indirect immunofluorescence microscopy were conducted on all the steaks. Treated steaks were significantly more tender than control steaks at the three postmortem times. Of the four treated groups, NaCl/phosphate steaks had the lowest WB shear values. Also, sensory evaluation results showed the NaCl/phosphate treated steaks were more tender than the control and CaCl[subscript]2-treated steaks at 3 days postmortem. It is thought the NaCl/phosphate-treated steaks were more tender because of increased WHC and juiciness values. Although tenderness was increased, bitterness was also noted in the CaCl[subscript]2-treated steaks. CaCl[subscript]2-treated steaks had higher MFI values, more rapid titin degradation, and an increase in the 30,000 dalton component. With the use of indirect immunofluorescence the degradation of the titin molecule by 3 days postmortem was observed. These observations are indicative of calcium stimulated proteolysis by the calpains to enhance tenderization. The NaCl/phosphate, and CaCl[subscript]2 injected steaks had similar palatability and physical/chemical values at 13 days postmortem. Consequently, early postmortem treated steaks (3 days) offer greater palatability benefits, than subsequent postmortem aging times (13 days). Because CaCl[subscript]2 injected steaks imparted a bitter sensation, this bitterness attribute could likely prohibit the commercial use of CaCl[subscript]2 injection to enhance tenderness. Therefore, our results suggest the use of NaCl/phosphate injections would offer greater commercial and consumer advantages than CaCl[subscript]2 injections.