In 1990, NSW Fisheries initiated a mass selection programme in Port Stephens, NSW, with the aim of breeding faster growing Sydney rock oysters Saccostrea glomerata (Gould 1850). After two generations of selection, an average weight for age advantage of 18% (range 14–23% per breeding line) was achieved. This equates to a reduction of 3 months in the time taken to reach market size. Experiments are planned to determine how much of this 3 months advantage is additive to the 6 months advantage this laboratory has already obtained using triploid S. glomerata. A parallel set of S. glomerata breeding lines was established on the Georges River, NSW, to include selection for resistance to the protistan parasite Mikrocytos roughleyi, the causal agent of winter mortality. The programme was disrupted by the outbreak of QX disease Marteilia sydneyi, another protistan parasite, in 1994. In 1997, the breeding programme was reorganized and expanded. New lines were bred from oysters that had survived both QX and winter mortality. After one generation, a small improvement in resistance to QX has been recorded; however, the exposure of further generations to M. sydneyi will be required to confirm an increase in resistance.