Synthesis and antiimplantation activity of variously substituted 2,2-dialkyl-3,4-diphenylchromenes and 3,4-cis- and trans-chromans derived from them are described. Pregnancy-inhibiting activity in rats was exhibited by a number of these compounds, which was particularly marked in the case of 3,4-trans-3-phenyl-4-p-(beta-pyrrolidinoethoxy)-phenyl-7-methoxychroman (32), the corresponding 2,2-dimethyl analog 34, and 3-phenyl-4-p-(beta-pyrrolidinoethoxy)phenyl-7-methoxychromene (26). The structure-activity relationship of these compounds is discussed.