The degradation of guanosine 5'-diphosphate,3'-diphosphate (ppGpp) by the "crude" ribosomal fraction of Escherichia coli CP78 (rel+, spoT+) was demonstrated and characterized. When the 3'-pyrophosphoryl group of ppGpp was hydrolyzed, the primary degradation product was 5'-GDP. Phosphorylation of ppGpp to guanosine 5'-triphosphate,3'-diphosphate (pppGpp) prior to degradation was not necessary. The degradation process required Mn2+ and was inhibited by EDTA. Levallorphan, an inhibitor of in vivo ppGpp degradation, also inhibited ppGpp degradation by the crude ribosome. Thiostrepton and tetracycline did not have any inhibitory effect, indicating that the reaction is not a reversal of pyrophosphorylation catalyzed by the stringent factor/ribosome complex. Crude ribosome fractions from E. coli NF161 and NF162, both spoT-, contained little degrading activity, but similar fractions of E. coli CP79, a relA- and spoT+ strain, contained ppGpp degrading activity.