This paper describes research on twins. Several couples have been observed pre-natally with the aid of ultrasound and subsequently with the method of infant observation as described by Bick.

First I mention the mythology surrounding twins and the classical literature on twin studies. A description of the research follows and two examples are given to illustrate how early markers of individual temperament can already be observed in the womb. Each twin seems to have its own temperament from the very early stages and each couple seems to establish a characteristic pattern of behaviour very early on. Both temperament and behaviour of the couple seem to continue in the same direction after birth.