The first appearance in print of Fleming’s announcement of his epochal discovery of the antibacterial properties of penicillin in 1928, one of the greatest and most beneficial medical discoveries of all time. Fleming did not, however, succeed in making penicillin the chemotherapeutic agent it is today, a task which was not fulfilled until some fifteen years later by Howard Walter Florey and Ernst Boris Chain and their collaborators. They determined that penicillin was by far the most powerful microbe-killer yet discovered – it was found capable of inhibiting some kinds of bacterieal growth at a dilution of one part in 50 000 000 – and they set themselves the ardous and elusive task of isolating its active principle, elucidating its chemical structure, and producing it in a laboratory. In 1945 the Karolinska Institutet decided to award the Nobel Prize jointly to Fleming, Chain and Florey ”for the discovery of penicillin and its curative value in a number of infectious diseases.” Fleming’s original offprint is a legendary rarity: fewer than five copies are thought to have survived from the original printing of about 150. It has an orange wrapper with printed title stating in the upper right corner: ”Reprinted from The British Journal of Experimental Pathology, 1929, vol. X, p 226”. When further work by Chain and Florey revealed the true efficacy of penicillin, Fleming was so deluged with requests for copies of his original article, that he had a new separate edition of about 250 copies printed in 1944, which is easily confused with the original. It is thought that Fleming got about 100 offprints of the 1929-paper and that many of those he distributed to colleagues and institutions were thrown away between 1929 and 1941 before the work was recognized as being important. A copy of the original offprint (at least the reprint) may also have been sent to the Nobel Committee, who in turn entrusted their offprints to the Karolinska Institute Library, but is unfortunately not traceable today. Collation: Complete volume X (1929), pp viii, 407. Fleming’s paper: pp 226-236 with one plate with four figures. Binding: Rebacked red half cloth. Library binding. References: Garrison-Morton 1933; Grolier, One Hundred Books Famous in Medicine, 96; Norman 798; Printing and the Mind of Man 420a; Friedman & Friedland, Medicine’s 10 Greatest Discoveries No 9; DSB, V, pp 28-31; Ernst Weil, Catalogue 31 (1963), 278.