Sequential hemodynamic and biochemical changes were studied in 24 infants with sepsis due to beta-hemolytic streptococcus to define the temporal patterns of physiologic events and to compare them in surviving (n = 11) and nonsurviving (n = 13) infants. Septicemia was documented by positive blood culture in all. Biophysical and biochemical measurements were obtained before and hourly, for 11 h after antibiotic therapy was initiated. Surviving infants had significantly higher Hct and systolic and mean arterial pressures than nonsurvivors. In nonsurvivors, low BP was associated with a concomitant rise in CVP and severe metabolic acidosis refractory to therapy. Although there were no differences in PaO2 or PaCO2 between survivors and nonsurvivors, arterial-alveolar oxygen gradients were significantly greater in nonsurviving infants. These data show cardiorespiratory and metabolic alterations that differentiate surviving and nonsurviving infants with beta-hemolytic streptococcal septicemia.