Most semen is somewhat viscous. Liquefaction should be complete before viscosity is assessed.

Semen viscosity can be determined by trying to draw the specimen into a wide bore pipette. Normal semen can be dropped from a pipette in single droplets. Some laboratories report viscosity on a scale from 0-4. Others report the results as "non-viscous", "slightly viscous", "very viscous" and so forth.

A specimen that is more viscous than normal after liquefaction may have reduced sperm motility. During sexual intercourse, hyperviscosity can prevent the sperm from reaching the cervix.