This study was designed to investigate male and female interest in babies at middle childhood and adolescence. A total of 64 middle class subjects (half 8- to 9-years-olds, half 14- to 15-year-olds) were observed individually in a 6-minute waiting room situation with an unfamiliar 6- to 10-month-old baby and mother (confederate). While the subject was unoccupied, his/her interest in the baby was observed. Each subject later filled out a sex-role self-concept questionnaire, operated a slide projector which controlled the length of time each of 30 pictures was exposed and reported the five pictures liked best. Results indicated that middle childhood girls and boys were similar in the degree and nature of interest they exhibited in babies and that sex differences began to emerge in adolescence when the girls showed a trend to greater responsiveness to babies, chose more pictures of infants among their favorites, and spent a larger percentage of their time looking at baby pictures than adolescent males. Adolescent girls also reported more enjoyment in caring for infants and felt more comfortable with the responsibility for infants than did adolescent males. Findings by age group indicated differences between middle childhood and adolescence in the mode of responsivity. Children in middle childhood were as interested in the infant as adolescents, but did more looking and less approaching in the presence of an unfamiliar baby; adolescents were less inhibited and displayed their interest more overtly. It was concluded that by adolescence, girls have adopted sex-stereotypic values such as baby interest into their behavioral repertoire. (JMB)