Infection of Vero (monkey) cells by Germiston bunyavirus is highly cytopathic with cell lysis and virus production at a high titre, whereas infection of Aedes albopictus C6/36 (mosquito) cells leads, after an acute primary phase, to a persistent non-cytopathic infection with a loss in virus production. In this report we demonstrate that single-stranded RNA probes can be successfully used in an in situ hybridization assay to quantify viral expression during this persistent infection. The steady-state levels of viral S-RNA segment (genomic and messenger sense) during the acute phase were similar to those observed in lytically infected Vero cells, but appeared delayed. Both senses of S-RNA were detected throughout persistent infection but in lower amounts, in less than 10% of the cells and always in the cytoplasm of infected cells. The number of copies per cell of messenger sense S-RNAs remained low during persistent infection whereas a higher fluctuation was observed for genomic S-RNAs. In situ hybridization with specific stranded RNA probes provides both qualitative and quantitative informations, that can lead to a better understanding of virus-cell interactions.