SUMMARY—Four porcine muscle fiber types were determined on the basis of histochemical tests. Lightweight boars had a significantly higher percentage of β‐hydroxybutyric‐dehydro‐genase‐positive fibers in the longissimus dorsi than did gilts. Heavyweight boars had significtanly more esterase‐positive fibers in all muscles sampled (except gluteus medius) and significantly more β‐hydroxybutyric‐dehydrogenase‐positive fibers in the longissimus dorsi than either barrows or gilts. The number of esterase‐positive fibers in all four muscles from boars tended to be higher in the heavyweight than in the lightweight group, with the difference being significant for the dark biceps femoris. The trend between weight groups was opposite for all muscles from barrows and gilts. The quantity of intramuscular lipid in the longissimus dorsi increased with slaughter weight and tended to be lowest in the boars. It was postulated that the tendency for a greater accumulation of intramuscular lipid in the longissimus dorsi muscle of barrows and gilts than in boars could be attributed partially to the smaller percentage of fibers positive for enzymes (esterase and β‐hydroxybutyric dehydrogenase) necessary in removing lipid from muscle. Differences were noted between light and dark muscles in the distribution a
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