This pilot study examined the safety and efficacy of sufentanil in the ventilated neonate. Informed parental consent for study participation was obtained for eight infants who were admitted to the neonatal intensive care unit and required analgesic/sedative therapy as part of their medical management to support mechanical ventilation. An intravenous loading dose (0.2 microgram/kg) was administered over 20 minutes, followed by a continuous infusion (0.05 microgram/kg/hour). Whole blood samples were collected prior to onset of sufentanil therapy, immediately following the loading dose, and 24 hours after the start of the continuous sufentanil infusion for analysis of beta-endorphin and sufentanil serum content. Heart rate, respiratory rate, and blood pressure were recorded as a routine part of medical management. The ventilatory efficiency index (VEI) and ventilation index (VI) were calculated before and after sufentanil therapy. Four male and four female infants were admitted to this study; the mean gestational age was 37 weeks, and weight was 2,970 gm. Sufentanil therapy appeared to be well tolerated, as evidenced by a lack of nursing observations noting changes in heart rate or mean arterial pressure. VEI values increased in four subjects, and VI values decreased in six subjects. Overall, the mean increase in VEI was 19 percent; the decrease in VI was 27 percent. The beta-endorphin serum content decreased in all subjects, and nurses did not report any signs of patient discomfort. Serum sufentanil content was undetectable. Sufentanil appears to be a suitable agent to provide analgesia/sedation in the neonatal patient under the experimental conditions of this study.(ABSTRACT TRUNCATED AT 250 WORDS)