A determination-key is suggested, which can used for interpretation of "Bunte Reihe". In the first step seven reaction will tested (dextrose-gas-formation, acid-production from lactose, H2S-formation, urease-activity, indol-formation, motility, LDC-activity). The resulting pattern of reaction leads into a codenumber (Table 1). Table 2 shows a list with species/Genera for each pattern of reaction. Are two or more species in the ascertained codenumber, it is necessary to make further tests. They can have selected and interpreted by using table 3 (second step). The main advantages in use of this two-step determination-key for Enterobacteriaceae are: 1. By selection of a higher confidence level as used in most other determination-tables, together with coding the pattern of reaction, the interpretation of "Bunte Reihe" is easy. 2. Subjective and objective errors by interpretation of reactions will prevented. 3. For single reaction is fixed a time up to two days. In comparison with many other methods it brings a shortening of differentiation time in most cases. 4. It isn't necessary to buy an expensive commercial diagnostic-system. The usual "Bunte Reihe" media can used successfull. 5. Because of elimination of subjective interpretation it is possible to compare the results of laboratories, which works by using this determination-key.