Sulforhodamine 101 (SR101) is a red fluorescent dye.

In neurophysiological experiments which comprise calcium imaging methods, it can be used for a counterstaining of astrocytes to be able to analyze data from neurons separately.

[1] However, in addition to labeling astrocytes, SR101 labels myelinating oligodendrocytes.

[2] SR101 has been reported to affect excitability of neurons and should therefore be used with caution.

[3] A sulfonyl chloride derivative of sulforhodamine 101, known as Texas Red, is used for conjugation to a number of functional groups, especially primary amines.