Alkaline alcohol with ammonia (90/10) is a chemical solution consisting of 90% alcohol (usually ethanol or isopropanol) and 10% ammonia solution. This mixture is often used in histology and cytology.

The alkaline property of the solution results from the ammonia component, which increases the pH of the solution. This property enables the removal of acidic dyes from cells or tissues in certain staining methods.

Alkaline alcohol with ammonia (90/10) is often used as a destaining solution in staining procedures such as Gram staining. In this staining method, bacteria can be distinguished into Gram-positive and Gram-negative bacteria based on their cell wall structure. After staining with crystal violet and Lugol's solution, the alkaline alcohol is used with ammonia to selectively remove the color from Gram-negative bacteria, while Gram-positive bacteria remain stained purple.