SUMMARY
Ontogenetic research is indispensible for a psychology of personality but has so far been hampered by serious methodological weakness. Hierarchical models of personality are a direct consequence of the ontogenetic approach. In order to serve rational purposes, these models need a firm methodological basis as a complement to ontogenetic methods. Percept-genetic techniques may be useful here because they combine exactness with a genetic approach to personality. In percept-genetic experiments data are presented in a sequence corresponding to the hierarchy of individual functions and thus, in principle, to the direction of personal growth.