In the staining of leucocytes successful use has be en made in this Department of the method described by Field (1941) in the demonstration of malarial parasites in thick films. The methylene blue solution is made up according to the formula of Hitch (quoted by Field). In the staining of these films the procedure of Field is modified so that the red cells are left intact and stained. The method as carried out is as follows. The two solutions of stain are mixed as required in the proportion of 6 drops of the methylene blue solution to 2 drops of the eosin solution and with the addition of 10 drops of buffered water at about pH 6.4. The mixture is then thoroughly shaken. The blood film is fixed with pure, acetone free, methyl alcohol for 10 seconds. The alcohol is then run off and the stain mixture applied to the slide with a pipette. Staining is continued for 10 minutes after which time the film is washed by waving about in a beaker of the buffered water at pH 6.4 for a few seconds. This method stains the leukocytes very clearly and is not subject to the several difficulties in using alcoholic solutions especially in the tropics.