Resinite samples from Latrobe Valley brown coals in the Yallourn, Yallourn North Extension, Loy Yang and Morwell open cuts were examined by C-13 high-resolution solid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy and laser ablation Fourier transform ion cyclotron resonance. A sample of bed-moist Yallourn resin, subdivided on the basis of colour, was also examined using these techniques. The yellow and black resinites contain more alcohol and aldehyde/ketone functionality and less carbon in exocyclic double bonds than the brown resinite. There also appears to be a change in the two types of carboxyl groups identified by n.m.r. spectroscopy. A friable resinite isolated from the Yallourn seam also exhibits signs of oxidation, as evident from carboxyl ratios. Resinite samples from Yallourn North Extension and Loy Yang open cuts show a marked reduction in carboxyl carbon compared with those from the brown sample from the Yallourn open cut. Latrobe Valley resinites have previously been described as being mainly polycommunic acid, formed by polymerization across the C-12, C-13 or C-14 C-15 double bonds. The Morwell resinite has greatly reduced exocyclic double-bond functionality relative to the Yallourn brown resin and cannot be described by this polycommunic acid model. It is also concluded that polycommunic acid is a poor model for many of the Yallourn resinites since they have different structures.