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Toughness of poultry breast muscle was influenced by the rate of rigor onset, the rate of cooling and chilled storage time. The pH of the breast muscle at 20 min after stunning (pHzo) in 52-day-old chickens varied from 5.9 to 6.9, and in 70-day-old turkeys from 6.2 to 6.8. In turkey meat with pHzO > 6.4, toughening was induced by immersion chilling to 7°C within 65 min post mortem and subsequent 'tanking' in iced water. Unaged, thawed meat from chicken carcasses, in which freezing commenced about 2 h after stunning was tougher than that from carcasses chilled for 16 h before freezing. Both were tender after 7 days chilled storage. Electrical stimulation of carcasses using 94 V decreased pH20 by an average of 0.3 unit in turkey, with no overall increase in tenderness. In chicken, it decreased the pHzO by 0.5 unit, but caused an overall toughening due to increased rigor shortening in carcasses with pH20 < 5.8.