The National Library of Medicine (NLM) has long been a world leader in the archiving and distribution of the print-based images of biology and medicine. NLM has also been a pioneer in the use of computer systems to encode and distribute textual knowledge of the life sciences. NLM's Long Range Planning effort of 1985-86 foresaw a coming era where NLM's bibliographic and factual database services would be complemented by libraries of digital images, distributed over high speed computer networks and by high capacity physical media. The NLM Planning Panel on Electronic Imaging recommended that NLM should undertake the building of a digital image library consisting of computer-assisted tomography (CAT), magnetic resonance interferometry (MRI), and cryosection images of a representative, carefully selected and prepared male and female cadaver--the "Visible Human Project." The male Visible Human data set is now being made available through a license agreement with the NLM. A wide range of educational, diagnostic, treatment planning, and commercial uses is predicted. The Visible Human data set and its associated identification maps will serve as a "Boston Teapot" for medical imaging, a common public domain data set against which all medical imaging algorithms can be tested, and a cornerstone for future sets of related image libraries.