Under the balanced condition of growth of E. coli cells, no distinct difference is observed in stable RNA and protein synthesis between CP78 (rel+) and CP79 (rel minus), whereas a considerable difference is present in RNA accumulation between NF161 (rel+) and NF162 (rel minus), where NF161 smaller than NF162. The RNA content of NF161 is lower than that of NF162 in four different cultures with different growth rates. These two sets of isogenic pairs of rel+ and rel minus strains are commonly used in the study of rel gene function; however, NF161 is a mutant in the spoT gene whose product may be responsible for the degradation of ppGpp. The basal levels of ppGpp in these four strains growing with three different growth rates were examined: NF161 (rel+ spoT minus) has a much higher content of ppGpp than do other strains. Furthermore, the contents of ppGpp tend to be lower when the above four strains are growing at a faster rate. Thus a close correlation seems to exist between the content of RNA and the basal level of ppGpp under the condition of balanced growth.