Since opinions differ as to whether the oxidative and glycolytic capabilities of skeletal muscle are altered in acute infection, enzyme activities in oxidative, glycolytic and degradative (acid hydrolases) pathways and total protein and DNA were determined in skeletal muscle of rats infected with Streptococcus pneumoniae, Salmonella typhimurium or Francisella tularensis. Studies were performed separately in red (slow twitch) and white (fast twitch) muscle tissue because these fibers function during different types of exercise. In the salmonella- and tularemia-infected rats, the intramitochondrially located oxidative enzymes of muscle were decreased to 56-83% of controls whereas the glycolytic enzyme situated in the cytosol showed an earlier and more pronounced loss of activity, 30-75% of controls. In the pneumococcal infection, only reduced glycolytic activity was significant. DNA concentrations were unchanged in any infection. Reductions during tularemia were statistically correlated with whole-cell protein degradation, while that of the glycolytic enzyme was parallelled by activation of lysosomal enzymes. Red and white muscle tissues responded similarly, in contrast to several other pathologic states that involve a catabolic component of muscle with a predominant response (or damage) in one or the other fiber type.