The authors compared the oxygen consumption in platelets from the umbilical cord blood of 36 healthy newborn infants with that of 27 adult subjects, before and after thrombin addition (1.67 U/ml). Oxygen consumption at rest was 6 mumol/10(9)/min in adult control platelets and 5.26 in newborn infants. The burst in oxygen consumption after thrombin addition was 26.30 mumol/10(9)/min in adults and 24.90 in infants. Dinitrophenol did not inhibit the burst of O2 consumption in platelets in 8 out of 10 newborn infants, while the same concentration caused a decrease in 9 out of 10 adult subjects. Deoxyglucose inhibited the burst in O2 consumption in newborn infant and adult platelets by about 50%. KCN at the concentration of 10(-4) M completely inhibited basal oxygen consumption but did not completely inhibit the burst after thrombin. At the concentration of 10(-3) M, it inhibited both basal O2 consumption and the burst in infants and adult subjects.