As the title suggests, this is a reference directory of 795 on-line databases in the medical and life sciences. There are 686 entries that describe type, subject, producer, on-line service, conditions, content, language, coverage, time span, and update frequency. The directory includes an introduction to on-line databases plus guidelines for selecting and using bioscience databases. The addresses of the services and gateways are provided, and there are indices by subject, service and/or gateway, and title. Clearly, this is a valuable reference work for persons working in this field. The authors also produce a Directory of Databases [1] of which this a subset.