The purpose of this study was to investigate the phenomenon of choral blend through acoustical analysis of individual vocal sounds. One aspect of the study involved identifying and comparing the acoustical qualities of sounds produced in the usual solo manner and sounds produced by the same singers attempting to blend with a unison ensemble. Another aspect of the study involved identifying and comparing the acoustical qualities of vocal sounds identified as blending well and poorly with a unison ensemble. Singers attempting to blend adjust their overall intensity not only to affect the perceived loudness of their tones, but also to facilitate other acoustical changes which are helpful for achieving blend. Vocal blend apparently may be achieved more readily on vowels having few upper partials than on vowels having numerous upper partials. Where vibrato is employed, certain vocal sounds can achieve a good blend even though their fundamental frequencies only approximate the theoretically correct frequency. There apparently is an interaction between the vibrato of a vocal tone and its spectral features, making it advantageous for the singer to adopt mutually beneficial approaches to both factors in order to blend. Vowel modification effective for achieving vocal blend- -at least for sopranos-- appears to consist primarily of changes in the intensity relationships between the vowel formants. Singers' variations in frequency extend beyond the boundaries of any system of tuning or temperament.