SUMMARY: A quantitative study of the survival of vegetative bacteria on drying in various suspending media led to a simple method for preserving bacterial cultures. Bacterial cells are suspended in melted nutrient gelatin cont.aining ascorbic acid or sodium ascorbate in concentration of 0.25-0.5 yo. Small quantities are dried over P,O, at pressures of 100-300 mm. of mercury and stored in vucuo over P,O, at room temperature. A wide range of bacterial species of medical and veterinary importance was preserved by this method for 4 years. The slow decline in the number of viable organisms and the high percentage survival rate at 4 years indicate the likelihood of survival for a much longer period. The virulence of a number of pathogenic species was successfully maintained in the dry preparation. The method might well be applied to the preservation of living vaccines. The survival rates with Chromobacterium prodigiosum dried by this method were better than those in preparations subjected to rapid freeze-drying processes. They were, however, unsatisfactory with a few species such as Vibrio cholerae and Neisseria meningitidis. A number of methods have been described for the preservation of stock cultures of bacteria by drying. The simplest consists in drying the organisms suspended in culture fluid or resuspended in saline, serum or blood in a desiccator in vacuo over dehydrating agents such as H,SO, or P,O,. The suspensions are dried on sterile coverslips, filter paper, in small test-tubes, or more conveniently in sterile ampoules which can subsequently be sealed off in vacuo. Successful results with a variety of bacterial species have been reported by Heim (1905, 1907, 1922), Brown (1925, 1932), Harris & Lange (1933), Otten (1930, 1932), Pauli (1932), and Mackie & McCartney (1945). Some pathogens have also been preserved satisfactorily by similar drying of the spleens taken from infected animals. Others recommend freezing the bacterial suspension immediately before and during the drying process by immersing the container in an ice and salt mixture, or in a mixture of CO, snow and glycerol placed in the desiccator (Shackell, 1909; Rogers, 1914; Swift, 1921, 1937; Morton & Pulaski, 1938). A more elaborate freeze-drying process was developed by Elser, Thomas gt Steffen (1935) and Flosdorf & Mudd (1935, 1938) for the preservation of biological products, including micro-organisms. In this so-called ' lyophile ' process the bacterial suspension is delivered into ampoules and frozen by immersion in salt and ice mixture or CO, snow. The ampoules are then attached to a manifold and the moisture is drawn off by means of an efficient vacuum pump, such as the Cenco-Megavac or Hyvac, and trapped by condensation in a vessel immersed in CO, snow or by means of a chemical desiccant chamber containing anhydrous calcium sulphate. Traps containing P,O, are used also to