Since 1985, a number of influential studies on the economic effects of immigration have been based on the ORANI model of the Australian economy (eg Baker-CEDA, 1985: CIE-CAAIP, 1988: CIEBIR, 1990). The results have generally been interpreted as showing that the economic effects of immigration are favourable. Critics of the use of ORANI argue that the model's results are too dependent on assumptions built into the model or imposed for particular experiments. This paper considers the influence of the assumptions on the results in the studies and reports results from simulations with alternative assumptions.