The estimates were derived from existing secondary data sources and from research findings on the extent of drug abuse in the U.S. and the association between drug abuse and other types of behavior that have their own implicit costs. Direct costs of drug abuse are those expended on, or arising from, law enforcement, the judicial system, nondrug crime, drug traffic control, drug abuse prevention, and housing stock loss. Indirect costs -- associated with absenteeism, unemployability, drug-related deaths, incarceration, and work lost due to drug treatment -- represent a loss to society of goods and services that would have been provided if the individuals involved had not been engaged in drug-abusing activities. The total estimated costs of drug abuse are separated here into those associated with heroin abuse and those due to the abuse of other drugs. The estimates of the cost of heroin abuse in fiscal year 1975 range from $4.5 to $8.3 billion, comprising approximately 62 percent of the total economic cost of drug abuse. 3 tables, 1 figure, and 16 references