The purpose of this exploratory descriptive study was to examine relationships among physiological stress signals (heart rate (HR), respiratory rate (RR), and oxygen saturation) and stress behaviors (6 stress behaviors related to sleep-wake states, 10 self-regulatory behaviors, and 17 behavioral stress cues) in preterm infants during periods of environmental stress. This research used a prospective repeated-measures design in a convenience sample of preterm infants of <37 weeks' gestational age and <28 days' postnatal age. All infants were in the incubator in a neonatal intensive care unit or a sick baby care unit in one of two hospitals at the time of data collection. Multiple linear regressions of generalized estimating equations were used to determine relationships. Variables were measured every 2 min over 4 hr, for a total of 4,164 observations in 37 preterm infants. There were statistically significant relationships between 9 stress behavioral responses and changes in HR (seven stress behaviors and two self-regulatory behaviors; p < .05), between 9 stress behavioral responses and changes in RR (seven stress behaviors and two self-regulatory behaviors; p < .05), and between 11 stress behavioral responses and changes in oxygen saturation (seven stress behaviors and four self-regulatory behaviors; p < .05). Findings demonstrate that the functions of self-regulatory behaviors and some special behaviors in preterm infants during environmental stress are related to physiological stress signals. However, results should be investigated further in larger samples.