Four releases of sterile Queensland fruit flies were used in Sydney to assess their flight and distribution characteristics. Flies were detected within 400 m of the release site but did not reach the 5 km trapping array. The distribution was more pronounced towards the north-east and it may have been linked with strong wind prevailing in that direction. CLIMEX was used to indicate that the distribution was not limited by adverse weather. The distribution tended to agree with the formula predicted by Meats (1998). Flies marked with orange dye resulted in the highest recapture rate compared with pink, green and blue dyes. The possible reduction in quarantine radius, following a declared outbreak, is discussed.