Viability is a measure of the percentage of cells that are alive. Since motile cells are inherently viable a viability assessment may not be necessary when motility is high. Most laboratories set a minimum motility after which a viability will also be performed.

To assess viability, place a drop of semen on a slide. Add an equal volume of a vital stain such as trypan blue. Cover with a coverslip. Allow color to develop for several minutes, but not more than 5 minutes. Count 100 cells (both motile and non-motile cells) on each of 2 slides. During the count differentiate between the white cells (living) and blue cells (non-living).