Glycation is a condensation reaction between reducing sugars and primary amino groups in proteins. It proceeds in many stages leading to formation of reversible Schiff bases, Amadori products and finally to irreversible products called advanced glycation end products (AGEs). Glycation is extensively studied in relation with diabetes and aging. Because of the common belief that it is a slow process under physiological conditions affecting long-lived proteins, until recently glycation has not been studied in prokaryotes. Our recent data, however, have shown that glycation takes place also in bacteria. The aim of this study is to check whether bacterial cytosol contains glycating compounds. Using histone H1 as a substrate for glycation, we show that the incubation of histone H1 (placed in dialysis bags) in bacterial lysates leads to accumulation of both early and late (AGEs) glycation products. This means that the glycating compounds of Escherichia coli are low molecular mass substances dissolved in bacterial cytoplasm.