SummaryEscherichia colibacteria produce at least one 70 kD stress protein, the product of thednaKgene. We have compared the rates of degradation of different types of abnormal proteins in nullIon E. coliwith a partial deletion of thednaKgene with the rates observed in nullIon dnaK+cells. We have found that both canavanyl proteins and puromycyl polypeptides are degraded more slowly in the nulldnaKmutants than in thednaK+strain. However, a temperature‐sensitive mutant Lacl protein is degraded more rapidly in the nulldnaKstrain. The stability of this temperature‐sensitive Lad protein was also examined in detail under various other conditi