Adaptive group testing in the presence of a large percentage of defectives
is best done by individual testing rather than by pooling. The fraction of
items which must be defective to make individual testing optimal remains un
known, and is conjectured to be 1/3. In this paper it is shown that when th
e number of items is sufficiently large, and the fraction of defective item
s is at least 1/log(3/2) 3, individual testing is optimal.