The content and the half-life of mRNA coding for the Ca2+-dependent metalloproteinase were measured by determining the enzyme activity excreted into the medium by cells pregrown in the absence of Ca2+ after addition of Ca2+ and actinomycin D. The content of the functional proteinase mRNA was highest at 31-degrees-C, which is the optimal temperature for the synthesis of this enzyme. Its half-life was 15 min, 7 min, and less than 2 min at 24-degrees, 35-degrees, and 42-degrees-C, respectively. Only the third of mRNA molecules synthesized at 31-degrees-C was translated in vivo into an active enzyme at 42-degrees-C, when compared with the translation proceeding at 24-degrees-C. Two-thirds of mRNA molecules synthesized at 31-degrees-C were translated into stable cell proteins at 42-degrees-C when compared with translation at 24-degrees-C. The mean half-life of mRNAs coding for cell proteins was 6-7 min at 24-degrees-C, 3 min at 35-degrees-C, and 2 min at 42-degrees-C.