Human populations have been studied for variability in attractiveness to mosquitoes [Aedes aegypti var. queenslandensis (Theobald)]. Attractiveness or its lack was quantitated in 2 ways: 1) by subjecting individuals to mosquito bites, and 2) by recording the time when 50% of exposed mosquitoes would probe on the bottom of a cage held over the forearm. This measurement we called probing time (PT50). With the biting technique 1 individual of 838 persons tested was found resistant to the bite of the mosquito. Persons highly attractive to mosquitoes could not be identified with this biting technique. With the technique of PT50, 6 persons were found very unattractive to mosquitoes and 3 highly attractive out of 100 other individuals tested. These individuals were each retested with 100 PT50 determinations after a lapse of 2–3 weeks. Three persons were confirmed as highly unattractive and 1 as very attractive. It was found that the same mosquitoes could be used for at least 100 PT50 determinations, making this a quick and reliable technique to establish individual differences in attractiveness to mosquitoes.