Ten full-term jaundiced infants were examined with the Brazelton Scale before, during and following phototherapy. They were compared with 10 non-jaundiced control infants examined at the same post-partum ages. All infants were appropriate for gestational age and free of perinatal complications other than hyperbilirubinemia. Differences on the orienting items of the Brazelton examinations (primarily visual orienting) were found prior to the onset of phototherapy or separation, and persisted for the length of the study. The greatest over-all differences were noted during phototherapy and separation from the mother, at which times the treatment group had lower scores on four of the six orienting items. They also had lower scores on muscle tonus, pull-to-sit and cuddliness while undergoing phototherapy, and poorer scores on orienting items, self-quieting and tremulousness were also evident three days following treatment. It is suggested that the differences found in mother-infant interaction following separation for the management of minor medical problems may be related to changes in infant behaviour which are already evident prior to separation. In the cases of jaundiced infants requiring phototherapy, these changes appear to be related primarily to hyperbilirubinemia. The possibility of these effects being prolonged or confounded by phototherapy or separation cannot be discounted.