  We report the identification of the optical counterpart of the X-ray
transient XTE J1550-564 described in two companion papers by Sobczak et al
(1999) and Remillard et al (1999). We find that the optical source brightened
by approximately 4 magnitudes over the quiescent counterpart seen at B~22 on a
SERC survey plate, and then decayed by approximately 1.5 magnitudes over the 7
week long observation period. There was an optical response to the large X-ray
flare described by Sobczak et al (1999), but it was much smaller and delayed by
roughly 1 day.
