A combined single subject and group design was used to investigate changes in heart rate and crying in response to a heel lance, non-invasive tactile stimulation and baseline periods in 10 male and 10 female infants, each in their second full day of life. Heart rate was measured with an electrocardiogram. Percentage of time crying was computed from observations of audiotapes. Results for individual subjects indicated that heart rate and percentage of crying were consistently increased by the heel lance but that there was often wide baseline variability in the two measures. Analysis of variance indicated that responses to heel lance were higher than responses to tactile stimulation which were in turn higher than responses to baseline for both heart rate and percentage of crying (P less than 0.01). No significant sex differences were found. It was suggested that the increases in heart rate and crying in the context of a tissue damaging stimulus indicated that the infants experienced pain and that pain in infants can be reliably measured in clinical settings.