The purpose of the present study was to investigate aspects of vibrato performance among high school and university string players. The main questions were to determine whether students consistently initiate vibrato in an upward or downward direction and whether players vibrate continuously when performing slurs. Forty high school and university violin and cello students played exercises that included tones performed with and without vibrato. We measured direction and magnitude of change when initiating vibrato, pitch levels of vibrated and nonvibrated tones, and duration of nonvibrato when performing slurs. Results showed that these high school and university players did not reveal consistent initial vibrato movements in either direction or magnitude. Performers vibrated both above and below conceived pitch, rather than only upward or only downward. All performers stopped vibrating during the transition between slurred notes. Mean duration of nonvibrato portions of university students (0.42 second) was slightly less than that of high school students (0.50 second). Implications of these results for string pedagogy are discussed. (Contains 3 figures.)