The sucking response was studied in 13 low-birth-weight (LBW) newborns and 17 normal-birth-weight (NBW) newborns. An electronic suckometer was used to measure maximum intensity pressure for the suction and expression components of the sucking response for four consecutive 15 sec intervals at 5, 15, 30, 45, and 60 min of life. At these times LBW newborns exerted mean suction pressures of 5.8, 8.7, 3.1, 7.8, and 9.3 mm Hg and mean expression pressures of 14.0, 11.9, 13.0, 8.5, and 5.0 mm Hg. NBW newborns exerted mean suction pressures of 2.1, 25.0, 34.0, 68.2, and 93.7 mm Hg and mean expression pressures of 4.6, 5.6, 7.3, 8.3, and 7.0 mm Hg. Positive correlations were found for both LBW and NBW infants between suction pressure and birth weight (p < 0.01) and gestational age (p < 0.01); for NBW infants between maternal parity and suction pressure at 5 min (p < 0.05); and for LBW infants between second stage of labor and expression pressure at 5 min (p < 0.05). No significant differences were found in sucking pressures based on race, sex, maternal medication, or the occurrence of prenatal, intrapartal, or neonatal complications. The results of this investigation demonstrate that the sucking response is present in most newborn infants, LBW as well as NBW infants, during the first hour of life. These data also suggest a relationship between the sucking ability of newborn infants and both crying and sucking experience.