This report offers some general principles which are helpful for designing and constructing a test for measuring musical aptitude of persons from various age groups. A discussion attempts to clarify the concepts used within the psychology of music. The basic structuralist principles favored by Gestalt psychologists and structuralists are also discussed. The report suggests that many abilities measured by musical aptitude tests are effects of musical experience rather than musical aptitude. The concepts discussed--creative musicality, musical memory, musical intelligence, the sense of tonality, the sense of rhythm, and the sense of harmony--can be tested for their consistency with musical behavior, their circularity, and their importance. The report indicates that there are seldom clear and simple answers to the questions about the domains of constructs in the psychology of music. The structuralist tradition in music psychology, which maintains that most of the meaning in music is its structure, stresses the following properties in any test of musical aptitude: (1) the test must measure the ability to conceive groups of relations; (2) the relations must be objective; (3) the relations must be relatively general; and (4) the items must be constructed so that there are substructures in them. Problem areas of research in musical aptitude are identified. (Author/DB)