The rapid and dramatic induction of heat-shock proteins is accomplished by regulatory mechanisms acting at many different levels. Here we review current knowledge of two cytoplasmic mechanisms employed during the response in the fruit fly Drosophila melanogaster. (1) Heat-shock messages are translated with high efficiency during heat shock while most normal cellular messages are inactive. Sequences in the 5'-untranslated leader of heat shock mRNAs govern their preferential translation. (2) The messages for heat-shock proteins are unstable at normal temperatures. During heat shock, however, they are very stable and accumulate in large numbers. Sequences in their 3'-untranslated regions play a major role in determining their stability.