In April, 1997, bacterial strains were isolated in New Zealand from tissues of cotoneaster plants with typical symptoms of fire blight, which had grown in the Royal Botanical Gardens in Melbourne, Australia. To determine the relationship among the isolated strains and known strains of E. amylovora, three Australian strains, two strains from Maloideae hosts in New Zealand and Ea321 (CNBP 1367; ATCC 49947), a weakly virulent strain from Belgium, were subjected to nutritional, molecular and pathogenicity analysis under blind coding. Analysis of their carbon utilization pattern by Biolog, suggested that the three Australian strains are E. amylovora. Polymerase chain reaction (PCR) of the Australian strains using primers (Bereswill et al., 1992) derived from pEA29 resulted in amplified bands, whose sizes correspond to those of the PCR products of most E. amylovora strains. Cleaved Amplified Polymorphic Sequences (CAPS) of 48 diverse E. amylovora strains were determined using two regions of the hrp gene cluster. The CAPS profiles of the Australian strains were identical to those of strains pathogenic to plants in the subfamily Maloideae, and present in North America, Europe, the Middle East and New Zealand, but different from strains pathogenic to Rubus species and those isolated in Hokkaido, Japan. PCR products of the intergenic region of the 1 6S-23S rDNA also indicated that the Australian isolates cluster with Maloideae-infecting strains of E. amylovora. Succulent shoot tips of apple and pear cultivars were inoculated with ca. lO cfu/ml of the six strains. Two Australian strains (now ICMP 13298 and 13299) infected all twelve apple and all three pear cultivars inoculated. The third (now ICMP 13293) infected three of twelve apple but all three pear cultivars inoculated. In general, the virulence of the latter Australian strain, as judged by percent lesion length, was less than that of the first two Australian strains and was similar to that of one New Zealand strain, and strain Ea321. Our results support reports that fire blight occurred in Australia, and indicate that the Australian strains are similar to Maloideae-infecting strains of E. amylovora analyzed previously from North America, Europe and the Middle East.