This study analyzes the effects of one environmental property, illumination, as part of a general program to isolate differential effects of specific properties of the novel environment on attachment behaviors in infants and young children. Attachment is operationalized into two response classes: (1) proximity to the mother, and (2) contact with her. Twenty female infants within each of 5 age groups (between 8 and 24 months) were randomly assinged to one of two experimental groups who were exposed to novel environments with high or low levels of illumination. Within each condition, subjects were observed in a series of six 3-minute eipsodes presented in a standard order for all infants. Analysis of results indicates that illumination does influence attachment behaviors, with the direction of the effect varying the type of attachment behavior involved. Discussion focuses on various theoretical interpretations of the data. (DP)