Hypotheses about the environmental variables that interact with constitutional factors in the development of schizophrenia or affective disorders include neurophysiological dysfunctions, which can be tested in a laboratory, as well as family interaction patterns and coping skills, which are currently being examined by accurate measurements outside the laboratory. Pooling data from different research projects provides a massive amount of information about the at-risk children so that it should become easier, in time, to isolate those variables that predict eventual breakdown. (54 pp.)