[Study of intellectual activity in twins. I. Developmental features].

The investigation of 234 twins and 100 singletons at the age from 7 till 16 years old was carried out by WISC method. The intellectual development of twins was established to fall behind singletons at the expense of lower level of verbal intellectual functions. It is due to organic changes of nervous system, arising as the result of the action of unfavourable factors during antenatal period. Slight asphyxia and prematurity as well as the order of birth do not exert essential effect on intellectual development of twins. Low weight at birth combines with lower intellectual index only in cases when lowering of weight is due to the action of unfavourable factors during intrauterine period. "Twins situation" apparently renders positive influence on twins intellectual activity during school are, distracting children's attention in cases of unfavourable psychological situation in family. Intellectual environment renders positive influence on intellectual development of twins.