The current study examined the concentration of mothers' peripherally produced oxytocin after close physical interactions with their biological and non-biological children. Each of 35 mothers and children participated in a computer game that promoted physical contact. In one interaction context, mothers interacted with their own children, and in the other context, mothers interacted with unfamiliar children. After the activity, urine samples were collected from the mothers and were assayed for oxytocin. Data from 26 mothers were available for oxytocin analyses. Oxytocin levels were higher among mothers following interactions with unfamiliar children than following interactions with their own children. Possible explanations for the differences in oxytocin levels across contexts are discussed.