A mild heat shock at 35 degrees C, which induces heat shock gene expression, greatly enhances survival and the recovery of protein synthesis in Drosophila cells after a higher temperature heat shock. The 35 degrees C treatment is also effective in preventing heat-induced developmental defects in pupae. We show here that the major larval mRNAs are present in approximately normal (25 degrees C) concentrations after a 40.1 degrees C heat shock whether or not the animals receive a pretreatment. This indicates that the pretreatment affects translation directly rather than messenger concentration. We also observe selective translation of heat shock messages and some 25 degrees C messages during recovery from heat shock.