Although drug use and abuse has been considered a critical social problem since the mid-1960's, research dealing with the topic often omits explicit definitions which might clarify drug abuse issues. Problems are encountered by researchers in the beginning stages of definition, involving the question of what constitutes a drug. Many drug surveys omit both alcohol and tobacco use, although they should be considered drugs because of their pharmacological properties. Other research problems arise in questioning the use of drugs in both medical and nonmedical situations. Two strategies which attempt to separate medical and nonmedical use either exclude medically taken drugs from surveys by the phrasing of questions or emphasize the source of the drugs. Studies on drug abuse have tried to measure its extent by analyzing the frequency and quantity of drug abuse. However, research which does not measure the schedule of use within a particular time period does not accurately reflect drug use patterns. Some studies have attempted to deal with the related subject of current use by identifying cycles of use or by abandoning the use of the word 'current' which implies continuity. The Total Drug Use Index has proved to be a valid instrument for measuring the degree of drug involvement. While frequency and intensity have been the focus of much research on drug abuse, some effort has been made to measure the method of administration. Other research questions arise in considering the issue of polydrug use, including measurements of the sequence of use and the consequential history of drug use. A total of 23 references are included. For the complete drug use and crime report, see NCJ 40293.