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Summarj. HaeHI andTaql restriclion digest profilesof cDNA to infected cell RNAor virion RNA were used as a guide lo gcnclic relationships between fouricen isolate of Ross River virus (RRV) obtained from mosquiiuescollccied in various localities in easiern Ausiralia where ihe virus '\s endemic. RRV isolates from t-iji. American Samoa, ihe Cook Islands and ihc W'allis Islands where major ouibrcaks of epidemic polyarthritis lonk place in 1979-19H0 were also examined.Among these RRV isolates we have identified three geneiic lypes (l-lil) on the hasis of differences between iheir restriction digest proHles. We estimate ihat IS-S^^o nucleoiide sequence diversity exists between genetic types. Within each genetic type strain dilTcrentiation gave rise to small but significant differences in restriction digest profiles.No clear pattern of geographic distribution of RRV genetic lypcs could bo established from the limited number of RRV isolates examined. Genetic types I. II and III, respocti\ei\. were isolated from three, three and one different mosquiio species, indicating there is no sirong association beiween geneiic type and thf species of mosquito vecior.Haelll restriction digest analysis did not detect any genetic difference between the four Pacific Island isolates, suggcstitig that a single RRV variani was involved tn ihe epidemics. Genetically, this variant was closely related to isolates of genetic type 11. Virtually identical Haelll restriction digest profiles were observed for isolates obtained at various stages of the Pacific Island epidemics, suggesting that extensive sequence evolution did not accompany Ross River virus .spread.

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