Our proposal is to study infants in the Neonatal Intensive Care Unit (NICU) who are undergoing a heel stick for blood sampling, a standard procedure in patient care. Currently, these infants do not get any pain relief for this procedure. Several recent clinical studies have shown the usefulness of nitrous oxide (laughing gas) for treating pain for minor procedures in children 0 to 18 years, but these effects have not been exclusively studied in the newborn and infant populations. Animal studies have questioned the anti-nociceptive (pain-blocking) effect of nitrous oxide in very young animals. It is unclear if this also applies to humans. The reason for this difference may be due to an immaturity of the neural pathways that modulate pain in the very young. The purpose of this study is to investigate whether or not nitrous oxide has an analgesic (pain-relieving) effect in infants undergoing minor procedures in the neonatal period (less than 3 months).