The influence of ante-mortem stress on rigor mortis development was investigated in carp muscle. For this purpose, an isometric tension meter was constructed applying the interface assembly to the data acquisition. Immediately after death the stressed fish muscle generated strong contractile tension and entered the rigor state. Unstressed fish muscle maintained the relaxed state for an initial 21h. It then entered the rigor state and generated half the tension of the stressed fish. After both muscles generated the full rigor tension, they lowered gradually. No significant difference was detected between the residual tension values at 70h postmortem of both muscles. In stressed fish just after death, both the ATP/IMP ratio and the pH were lower when compared with unstressed fish. A more rapid decrease of the ATP/IMP ratio and the pH was found in stressed fish. When the pH reached the same value of 6.55, tension generation began irrespective of whether stressed or unstressed. At this stage, the ATP/IMP ratio was higher and more ATP remained in stressed fish. When the ATP/IMP ratio became close to the minimal value several hours after the arrival of ultimate pH, full rigor tension was generated irrespective of whether stressed or unstressed.