Developmental norms for young children's vocabularies have a number of applications in research design, assessment, and intervention, but have previously been very difficult to obtain. In the present study, month-by-month norms for comprehension and production of 396 words from 8 to 16 months, and production of 680 words from 16 to 30 months, were derived from a norming study of 1,789 children between the ages of 8 and 30 months using the MacArthur Communicative Development Inventories (Fenson et al., 1993). The norms are available in the form of a database program, LEX, for MS-DOS-based computers.