Areas of agreement and disagreement concerning intellectual developmental and the problems of mental retardation espoused by the author and by Uzgiris are discussed in this paper. The importance of environmental factors, along with the genetic and/or constitutional nature of the organism on which these environmental events impinge, is seen as central to the interactionist's position. A naive or premature environmentalist approach of the determination of development is asserted to be as erroneous as a naive or premature hereditarian approach. Considerable attention is devoted to the presentation of materials that highlight the importance of genetic factors in the interactionists' equation. The paper is considered (1) to insure that the reader never loses sight of the biological components of intelligence, (2) to point out that certain psychological functions may be more amenable to environmental manipulation than others, and (3) to highlight the issues that must be resolved before the manner in which environment affects both the intellectual and the non intellectual components of behavior is comprehended. (Author/AM)