The article discusses the question of application of the neuropsychological method in psychogenetic research. It is suggested to use neuropsychological indexes as endophenotype — an intermediate part between genotype and phenotype. Results of experimental study of mono- and dizygotic 43—62 year old twins are reported. Consideration of programming and control index (executive functions index) as an endophenotype has demonstrated that neuropsychological indexes may become a basis for the qualitative analysis of the intelligence structure.