Here we provide evidence that YbeY, a conserved heat shock protein with unknown function, is involved in the translation process. ybeY deletion mutants are temperature sensitive and have a significantly reduced thermotolerance. Nonetheless, there appears to be no damage of the protein quality control of mature polypeptides, as the levels of chaperones and proteases are normal and there is no accumulation of aggregates. Rather, the mutation results in a significant reduction in the level of polysomes, and upon a shift to a restrictive temperature (42 degrees C), there is an immediate and severe slowdown of translation. Taken together, the data indicate that YbeY is an important factor for bacterial translation even at 37 degrees C but becomes essential at high temperatures.