Mature human neutrophils from peripheral blood are known to be capable of limited protein biosynthetic activity. We now show that these cells are inducible for heat-shock protein synthesis when placed in short-term culture. Synthesis of hsp70 and hsp85 as well as the response to various temperatures and the time course of induction were typical for mammalian cell systems. This heat-shock response was blocked by actinomycin D added before heat exposure. This demonstration that hsp genes can be activated by heat exposure of terminally differentiated neutrophils supports the hypothesis that gene activation can serve a physiological role in these cells and opens up the possibility that synthesis of other gene products is similarly inducible.