[4] Mercury(II) bromide is used as a reagent in the Koenigs–Knorr reaction, which forms glycoside linkages on carbohydrates.

[5][6] It is also used to test for the presence of arsenic, as recommended by the European Pharmacopoeia.

[7] The arsenic in the sample is first converted to arsine gas by treatment with hydrogen.

Arsine reacts with mercury(II) bromide:[8] The white mercury(II) bromide will turn yellow, brown, or black if arsenic is present in the sample.

[9] Mercury(II) bromide reacts violently with elemental indium at high temperatures[10] and, when exposed to potassium, can form shock-sensitive explosive mixtures.