Tioman virus (TioPV) and Menangle virus (MenPV) are two antigenically and genetically related paramyxoviruses (genus: Rubulavirus, family: Paramyxoviridae) isolated from Peninsular Malaysia (2001) and Australia (1997), respectively. Both viruses are potential zoonotic agents. In the present study, the infectivity, growth kinetics, morphology and morphogenesis of these two paramyxoviruses in a human neuronal cell (SK-N-SH) line were investigated. Sub-confluent SK-N-SH cells were infected with TioPV and MenPV at similar multiplicity of infection. These cells were examined by conventional and immunoelectron microscopy, and virus titres in the supernatants were assayed. Syncytia were observed for both infections in SK-N-SH cells and were more pronounced during the early stages of TioPV infection. The TioPV titre increased consistently (10(1)) every 12 h after infection. In MenPV-infected cells, cellular material was frequently observed within budding virions, and microfilaments and microtubules were abundant. Viral budding was common, and extracellular MenPVs tended to be more pleomorphic compared to TioPVs, which appeared to be more spherical in appearance. The MenPV cytoplasmic viral inclusion appeared to be comparatively smaller, loose and interspersed with randomly scattered circle-like particles, whereas huge tubule-like cytoplasmic inclusions were observed in TioPV-infected cells. Both viruses also displayed different cellular pathology in the SK-N-SH cells. The intracellular ultrastructural characteristics of these two viruses in infected neuronal cells may allow them to be differentiated by electron microscopy.