A collection of the Nobel lectures delivered by the prizewinners in physiology or medicine for the period 1996-2000. Each lecture is based on the work for which the laureate was awarded the prize. The following is a list of the Nobel laureates during 1996-2000 with a description of the works that won them their prizes: P.C. Doherty and R.M. Zinkernagel (1996) - for their discoveries concerning the specificity of the cell mediated immune defence; S.B. Prusiner (1997) -for his discovery of "prisons - a new biological principle of infection"; R.F. Furchgott, L.J. Ignarro and F. Murad (1998) - for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system; G. Blobel (1999) - for the discovery that "proteins have intrinsic signals that govern their transport and localization in the cell"; A. Carlsson, P. Greengard and E.R. Kandel (2000) - for their discoveries concerning "signal transduction in the nervous system".