Regulation of new technologies to protect public health and the environment assumes that the regulators have adequate information with which to make informed decisions. In the case of DDT, however, full information on its effects did not become available until two decades after it came into widespread use. This situation arose for a variety of reasons. For some years, scientists lacked analytical tools to measure quickly small concentrations of residues (a minor problem). The organization and funding of science diverted attention from long range basic studies to immediate problems, and DDT seemed to pose no obvious hazard. Most important, past experience proved to be an inadequate guide to research on DDT's effects - a consequence of the novel chemical and physical properties of the material.