With the introduction of obligatory registration of twins in Budapest on 1 January 1970, our team started the genetic and somatopsychic examination of twins. The program is being carried out in collaboration with the institutions of the Child Health Care Organisation of Budapest and the National Institute of Public Health.

Since 1 January 1970, the placentae of twins born in Budapest are submitted to pathologic and histologic examination, and the twins living in Budapest are examined systematically by our clinical group at the age of six months, and one, two, and three years.

In addition to studying the social environment, examinations are carried out with regard to pediatrics, anthropometric measurements, photographic documentation, dental examination, dermatoglyphics, cardiology, and neuropsychiatry. In order to define the genotype of the twins we used haptoglobins and blood groups.