This study investigated the effect of day care attendance on the receptive and expressive language development of nine 4-year-old children. Five children who had 2 years of day care experience comprised a day care group. A home-reared group was composed of four children who had 3 months of day care experience. Children's receptive language ability was measured by the auditory comprehension items of the Preschool Language Scale (PLS), and their expressive language ability was measured by means of the verbal ability items of the PLS. Children's parents completed questionnaires that assessed the following variables that affect language development: (1) parents' education; (2) parents' income; (3) quantity and quality of language interaction in the home; and (4) children's birth order. The results revealed no differences in auditory comprehension between the two groups. The verbal ability scores of the day care group were slightly, but not significantly, higher than those of the home-reared group. Findings suggest that both home and day care environments are potentially rich in stimulating the language development of young children. Appendices include a day care center questionnaire, an informed consent form for parents, the parent questionnaire, the PLS, and a tabulation of the PLS test results. Contains 52 references. (Author/SM)