N-acetyl-L-cysteine is used as a mucolytic therapy as well as for treating acetaminophen overdose. It can also be used for other biochemical applications. Karl Fischer titration can be used to determine the water content in N-acetyl-L-cysteine. Special solvent mixtures can be used to prevent unwanted side reactions in the Karl Fischer titration. The water content of N-acetyl-L-cysteine can thus be determined quickly and accurately, as is shown in this Application Note.