analogue of strain-by-treatment animal studies (Plomin & Hershberger 1991). The genotype of adopted children is inferred from their biological parents, and the environment is measured in the adoptive home. Individuals thought to be at genetic risk for a disorder, but reared in adoptive homes with different environments, are compared to each other and to control adoptees. This methodology has been employed by a number of research groups to document gene-environment interactions in a variety of clinical disorders: In a series of Iowa adoption studies, Cadoret and colleagues demonstrated that a genetic predisposition to alcohol abuse predicted major depression in females only among adoptees who also experienced a disturbed environment, as defined by psychopathology, divorce, or legal problems among the adoptive parents (Cadoret et al. 1996). In another study, depression scores and manic symptoms were found to be higher among individuals with a genetic predisposition and a later age of adoption (suggesting a more transient and stressful childhood) than among those with only a genetic predisposition (Cadoret et al. 1990). In an adoption study of Swedish men, mild and severe alcohol abuse were more prevalent only among men who had both a genetic predisposition and more disadvantaged adoptive environments (Cloninger et
