Herbicide resistant weeds are having a major impact on Australian agriculture In response to this new problem, "genetic engineering" techniques are being used to create new types of lupins which are resistant to non-selective herbicides which still kill the weeds In this study the economic value of such a transgenic lupin was investigated using a multiperiod bioeconomic model The model represents the wheat/lupin cropping system of Western Australia. The profitability of a wide range of weed control measures (both chemical and non-chemical) used separately and in combination with a transgenic lupin are compared with the current options available to farmers For the scenarios considered. it is found that a system involving a Basta® resistant transgenic lupin would have similar profitability to a system based on current lupin varieties employing Gramoxone® for crop topping. However, where a transgenic lupin is resistant to glyphosate, and is used in conjunction with windrowing of both crops, farm profit increases by 33 percent.