['Hospitalized preterm infants may experience pain and stress, and narcotics are often administered to lessen their suffering. However, prolonged narcotic therapy may be detrimental during neonatal brain development. Using a rat model combining neonatal stress and morphine, we found that neonatal morphine impaired adult learning. Here we describe a new mouse model examining lasting effects of neonatal stress and morphine.', 'We tested whether repeated neonatal stress and/or morphine exposure affects early neurodevelopmental or adult behaviors.', 'Five groups of C57/BL6 mice (1: untreated; 2: morphine (2 mg/kg s.c., b.i.d.); 3: saline, 4: stress + morphine; 5: stress + saline) were treated from postnatal day (P) 5 to P9. Stress consisted of daily maternal separation/isolation (08:00-15:00 h) with gavage feedings and twice daily exposure to brief hypoxia/hyperoxia. Developmental behaviors included righting (P5) and negative geotaxis (P9). Adult behaviors included elevated plus maze, morphine place-preference conditioning, and forced-swimming. Plasma concentrations of morphine (P7) and corticosterone (P9 and adult) were measured.', 'Neonatal stress or neonatal morphine alone impaired adult place-preference conditioning, but the combination did not (interaction p < 0.01). Adult basal corticosterones were reduced by neonatal morphine treatment. There were no substantial differences in elevated plus maze or forced-swimming times.'] Does neonatal stress or morphine treatment alter adult mouse conditioned place preference?