A new measure to assess behavioral, affective and somatic outcomes in the acute phase of bone marrow transplant is described. The Behavioral Affective and Somatic Experiences Scale (BASES) is a 38 item nurse-report instrument, with five subscales labeled Somatic distress, Compliance, Mood/Behavior, Interactions, and Activity. A series of pilot studies were conducted to refine the content of the BASES scale and to establish its psychometric properties in terms of internal consistency, inter-rater reliability, and validity. Internal consistency (Chronbach's alpha) for the subscales ranged from .742 to .902. Inter-rater reliability was good, with a median correlation between paired nurse observations of .866. A parent report version of the BASES scale has also been developed, and the finding of significant parent-nurse correlations provides preliminary evidence of the validity of the measure. Potential uses of the BASES scale in the pediatric BMT setting are discussed.