Abstract: A composition for assaying nitrites comprising a diazotizable amine, an acid component and a coupling component, wherein the coupling component is a compound of the following formula I: ##STR1## wherein R represents a hydrogen atom or a straight-chain alkyl group having 1 to 6 carbon atoms, such as a methyl, ethyl, n-propyl, n-butyl, n-pentyl or n-hexyl group and n represents an integer of 1 to 6, with the proviso that the sulfoalkyl group may be substituted with at least 1 hydroxyl group,or a water-soluble salt thereof as well as test devices carrying the composition. This composition is far more sensitive than conventional compositions for assaying nitrites. With this composition, for example, a trace amount of as small as 0.02 mg/100 ml of a nitrite to be detected in urine in the diagnosis of a bacterial infection such as urinary tract infection can be detected surely.