Fruit flies are a serious economic pest affecting horticultural production world-wide. Increasing coordination of activities between neighbouring countries and those countries involved in fresh fruit trade is leading to more effective regional management of the fruit fly pest. 1.1 ACIAR Research Projects. ACIAR has supported fruit fly research in developing countries since 1984. Two projects, based in Thailand and Malaysia, have generated significant scientific and economic outcomes. The total cost of these two projects was $1.7m (in 1996 dollars). Specific outcomes include: 1. A more detailed understanding of exotic fruit fly species, their host range, pest status and spatial distribution; 2. Increased interest in fruit fly management in Thailand and Malaysia and throughout the South Pacific; and 3. The demonstration of an effective protein bait spray technology. 1.2 Project Benefits. While the two ACIAR research projects carried out in Malaysia and Thailand between 1984 and 1993 have generated economic gains in these countries, considerable benefits have been realised in Australia. These benefits include: a saving of $0.76m because of the reduced time taken to carry out a delimiting survey following the papaya fruit fly outbreak around Cairns in 1995; a gain of $5.03m from the quicker realisation of papaya fruit fly eradication benefits; gains of up to $4m a year during the eradication of the papaya fruit fly from Australia as a result of continued access to premium fresh fruit export markets; and gains of up to $0.28m a year as a result of continued access to fresh fruit export markets during the eradication campaign rather than redirecting produce to the domestic market. 1.3 Economic Pay-Off. It was estimated that the two ACIAR research projects are likely to generate a net benefit, in present value terms, of nearly $10m (in 1996 dollars). This represents a return of over $9 for every dollar invested. The internal rate of return was estimated at 35%. Most of these benefits have already been realised, with over $7m in present value terms being realised to date.