In this study, longissimus dorsi lumborum (LDL) muscles obtained from 10 beef carcasses were used to determine the effects of temperature conditioning and citrus juice (CJ; Citrus aurantifolia) marinade on quality and microstructure of aged beef carcasses. After slaughter, the right sides of carcasses (RC) were rapidly chilled (air temperature, -20+/-1 degrees C; wind velocity, 2 m/s) for 6 h and then placed in a conventional chiller (air temperature, 2+/-1 degrees C; wind velocity, 1 m/s) for 18 h, while the left sides (DC) were delay chilled at 15 degrees C for 6 h and then at 1 degrees C for 18 h. At 24 h postmortem, LDL was removed from the each carcass sides and stored at 0-4 degrees C for up to 7 days postmortem. At 2 days postmortem, each portion was cut into 5 cm x 1 cm x 1 cm and all strips were randomly submitted to the marinade treatment using solutions containing 50% CJ and distilled water as control. The beef strips were immersed for 12 h in the marinade solutions (10 ml/g meat) at 4 degrees C before evaluating the water holding capacity (WHC), cooking loss (CL), shear force (SF), sarcomere length (SL) and color (L*, a*, b*). The results showed that RC and CJ marinade reduced CL and WHC. DC and CJ had a positive effect on SF and SL compared to RC. Phase contrast microscopic examinations showed that SL of the LDL are longer in the DC group. These results suggest that RC would be useful for applying together with CJ marination for improving the tenderness of beef meat.