The National Ambient Volatile Organic Compounds (VOCs) Data Base update is the result of an ongoing effort to gather, evaluate, and compile the measured concentrations of a large number of VOCs. Data on the observed concentrations of three hundred twenty (320) volatile organic compounds (VOCs) were compiled, critically evaluated, and assembled into a relational data base. Ambient (outdoor) measurements, indoor data, and data collected with personal monitors are included. The data are primarily from the period 1970-1987 and for locations within the United States. In order to compile data from many different sources, each concentration record in the data base represents the daily average for a single chemical, wherever feasible. The total data base contains more than 175,000 concentration records. The data have been assembled into a relational data base using dBASE III Plus, a commercially available data base management program. The data base is available on IBM PC-compatible diskettes. The available report contains a complete description of the data base files and a guide describing the use of a prepared program for searching and maintaining the data base. The data base consists of 42 files and requires 19.4 Megabytes of storage space.