Study the phototherapy effects on: transit time, lactose absorption and gut permeability. We study 109 newborns healthy during the first week of life, 73 jaundiced infants, 37 of them were treated by phototherapy during 57+-9 h. We use the tests of breath hydrogen (lactose and lactulose) and the test of gut permeability (polyethylene glycol PEG 600). Thus 81 infants, 27 in each group: control (CG), jaundiced (JG) and treated by phototherapy (PG). The results no significant difference was found. The conventional phototherapy lessened the fermentation activity of colonyc microflora, but didn't modify the "phisiology malabsortion of lactose", the mouthbto caecum transit time, neither the "anormal permeability" globally, although decreased urinary recovery of the higher molecular weight polymers.