The monograph arises from a technical review conducted on September 8 and 9, 1994, in Gaithersburg, MD, where 25 leading researchers presented papers on various aspects of the validity of self-reported drug use. The first section of this document is an overview of what is known about the validity of self-report based on studies using internal and external validity criteria. The second section focuses on methodological advances used or proposed as a means for understanding the extent of nonsampling error in surveys, and realizing further reductions in total error in estimates of drug use and associated behaviors. The monograph includes several articles detailing results of studies comparing drug use prevalence based on self-report, urinalysis, and hair- testing measures. Results from those studies must be viewed with caution in light of the limitations of hair-testing technology. References, tables, figures, notes