Minced beef meat was packaged under vacuum, air or oxygen, and pressurized at 10 ยฐC for 10 min. L* colour values increased significantly in the range 200-350 MPa, the meat becoming pink, while a* values decreased at 400-500 MPa, the meat becoming grey-brown. Simultaneously, total extractible myoglobin decreased in the range 200-500 MPa, while the proportion of metmyoglobin increased at the expense of oxymyoglobin at 400-500 MPa. Pressurization did not significantly increase the extractibility of heme iron by an acid solution. Packaging of meat under vacuum with an oxygen scavenger partly protected meat colour, since samples processed at 400 MPa became pink, without any change in a* value or metmyoglobin content. Blending chilled minced meat with NaNO 2 (and NaCl) 18 h before processing at 350-500 MPa afforded a similar protection. Cysteine, ascorbic acid, nicotinamide or nicotinic acid had no protective effects. Meat discoloration through pressure processing may result from (1) a 'whitening effect' in the range 200-350 MPa, due to globin denaturation and/or to heme displacement or release, and (2) oxidation of ferrous myoglobin to ferric metmyoglobin, at or above 400 MPa. Only the latter phenomenon is prevented by total oxygen removal or prior formation of nitrosomyoglobin.