The purpose of this study was to investigate possible influences of pitch register and dynamic level on vibrato rates and widths of university and high school violin and viola players. Analysis showed that pitch register significantly affected the vibrato rates and widths of the performers. Musicians vibrated 0.32 Hz faster and approximately 26 cents wider during high pitches than during low pitches. Dynamic level also significantly affected vibrato width. Performers increased vibrato width approximately 4 cents in the "forte" passages when compared to the "piano" passages. Furthermore, violinists demonstrated a tendency to vibrate slightly faster and wider than violists, and university performers varied their vibrato width to a greater extent between the "piano" and "forte" passages than did the high school performers. These results, along with further study, can contribute to the development of a systematic method for teaching vibrato. (Contains 2 figures and 2 tables.)