ABSTRACTThe effects of rotenone and pH on color of pre‐rigor muscle homogenates were determined by use of the Hunter Color Difference Meter and by visual appraisal. Both rotenone and low pH treatment led to development of bright red color in pre‐rigor beef muscle homogenates. Both effects are probably due to mitochondrial inhibition or inactivation, so that myoglobin remains oxygenated in presence of air. It is concluded that dark color of pre‐rigor muscle is due to oxygen consumption by actively respiring mitochondria at muscle surfaces, keeping myoglobin deoxygenated. It is likely that dark color associated with heat ring defect and dark cutting meat is also related to active mitochondrial respir