Trypan blue is commonly used in microscopy (for cell counting) and in laboratory mice for assessment of tissue viability.
The method cannot distinguish between necrotic and apoptotic cells.

It may be used to observe fungal hyphae and stramenopiles.

Trypan blue is also used in ophthalmic cataract surgery to stain the anterior capsule in the presence of a mature cataract, to aid in visualization, before creating the continuous curvilinear capsulorhexis.
In keratoplasty, trypan blue can be used to stain the posterior stromal fibers during deep lamellar endothelial keratoplasty (DLEK) and to stain the endothelium in Descemet’s stripping endothelial keratoplasty (DSEK).
Trypan blue is used in vitreoretinal surgeries also.

In early 20th century, the existence of a barrier protective toward the brain (blood brain barrier) was inferred, based on the observation that injection of trypan blue in animals led to whole‐body staining except for the brain and spinal cord.
Trypan blue is commonly used in microscopy (for cell counting) and in laboratory mice for assessment of tissue viability. The method cannot distinguish between necrotic and apoptotic cells.
It may be used to observe fungal hyphae and stramenopiles.
Trypan blue is also used in ophthalmic cataract surgery to stain the anterior capsule in the presence of a mature cataract, to aid in visualization, before creating the continuous curvilinear capsulorhexis. In keratoplasty, trypan blue can be used to stain the posterior stromal fibers during deep lamellar endothelial keratoplasty (DLEK) and to stain the endothelium in Descemet’s stripping endothelial keratoplasty (DSEK). Trypan blue is used in vitreoretinal surgeries also. 
In early 20th century, the existence of a barrier protective toward the brain (blood brain barrier) was inferred, based on the observation that injection of trypan blue in animals led to whole‐body staining except for the brain and spinal cord.
Trypan blue