A cDNA clone inducible by either a tumor promoter, 12-o-tetradecanoyl phorbol-13-acetate (TPA), or a T-cell mitogen, phytohemagglutinin (PHA), was isolated from a cDNA library constructed from the poly(A) + RNAs of TPA- and PHA-stimulated human tonsillar lymphocytes, and was named pLD78. Stimulation of the tonsillar lymphocytes with either TPA or PHA increased the amount of pLD78-specific RNA by about 10-fold, and simultaneous stimulation with TPA and PHA, by at least 30-fold. Analysis of the pLD78 cDNA sequence revealed that it codes for a polypeptide consisting of 92 amino acid residues, including a putative signal sequence. Moreover, the sequence of the 5' flanking region of the nuclear DNA encoding for the pLD78 cDNA showed a significant homology with the corresponding regions of the human interleukin 2 and immune interferon genes.