supravital stain

As the cells are alive and unfixed, outside the body, supravital stains are temporary in nature.

Those that enter and stain living cells are called supravital stains (e.g. New Methylene Blue and Brilliant Cresyl Blue for reticulocyte staining).

Very bulky or highly charged stains that don't cross live plasma membrane are used as vital stains and supravital stains are those that are either small or are pumped actively into live cells.

Partly due to their toxic interaction inside a living cell, when supravital stains enter a living cell, they might produce a characteristic pattern of staining different from the staining of an already fixed cell (e.g. "reticulocyte" look versus diffuse "polychromasia").

The most common supravital stain is performed on reticulocytes using new methylene blue or brilliant cresyl blue, which makes it possible to see the reticulofilamentous pattern of ribosomes characteristically precipitated in these live immature red blood cells by the supravital stains.