In coal petrology, fluorescence microscopy has mainly been used in the study of liptinite (exinite) macerals. Recently, its scope of application has been widened to investigate vitrinite. This paper describes the conditions under which inertinite can also be studied by fluorometry. The method makes use of relatively long-wave excitation. Although the strongest signals are received through a green exciter filter at 546 nm, blue light excitation (450–490 nm) is preferred because the fluorescence spectrum is broader, the microscopic image more polychromatic and maceral identification is easier compared with longer-wave excitation. Inertinite macerals are divided into fluorescent and non-fluorescent constituents on the basis of both visual distinction and relative intensity determinations at 650 nm measuring wavelength. It appears that fluorescent inertinite corresponds closely to reactive fractions determined by previous coking experiments.