Dialysates for the haemodialysis are produced unsterile and usually contain bacteria. Own investigations of bicarbonate dialysate and adequate initial solutions comprised sterility tests, determinations of the germ count and germ tolerance experiments. Only the "acid concentrate" was sterile. In the other solutions Corynebacteria, Acinetobacter and Pseudomonas bacteria dominated as typical water germs. In the fresh reverse osmosis water and the bicarbonate dialysate as well as in the recently produced 35-mmolar and 1-molar NaHCO3-solution the germ count was in each case about 10(5)/l and did not change itself essentially at room temperature within 6 hours. The "acid concentrate" and at a lower level also the 1-molar NaHCO3-concentrate have an antibacterial effect. The reverse osmosis water is the main contamination source for the bicarbonate dialysate, the application of which within 6 hours seems worth being used on account of the low germ count.