Highlights from this report include: for the period May, 1975, through April, 1976, there were 172,612 drug-abuse episodes reported at medical facilities involved in the Drug Abuse Warning Network (DAWN) Project that involved 246,524 drug mentions. Of the 172,612 drug-abuse episodes, 68 percent were reported in emergency rooms, 3 were by medical examiners, and 20 percent at crisis centers. Of the 246,524 drug mentions, 25 of the 3,000 substances mentioned accounted for 66 percent of all mentioned drugs. Data on demographics, motivation for drug use, source of substance, and employment status are presented for each type of medical facility and for each leading type of drug used. This report presents data on drug-abuse episodes and drug mentions collected through DAWN for the period May, 1975, through April, 1976, the fourth phase of the DAWN project. For this report, data were obtained from 984 hospital emergency rooms, county medical examiners, and crisis centers, located in 24 SMSAs (standard metropolitan statistical areas). DAWN is a large-scale, ongoing drug abuse collection system with several objectives: identifying substances associated with drug abuse episodes; monitoring drug abuse patterns and trends; assessing health hazards associated with drug abuse; and providing data for national, State, and local drug abuse policy and program planning. Tables and figures