Expression of the RI alpha subunit of type I cyclic AMP-dependent protein kinase (PKA) is increased in human cancer cell lines, in primary tumors, in cells after transformation, and in cells upon stimulation of growth. The sequence-specific inhibition of RI alpha gene expression by RI alpha antisense oligodeoxynucleotide results in the differentiation of leukemia cells and growth arrest of cancer cells of epithelial origin. A single-injection RI alpha antisense treatment in vivo also results in a reduction in RI alpha expression and inhibition of tumor growth. One injection was sufficient to inhibit tumor growth in mice for 2 weeks. The antisense DNA achieves this long-lasting effect by altering the balance between the production of PKA type I and a competitive molecule, PKA type II. Tumor cells behaved like untransformed cells by making less protein kinase type I. The RI alpha antisense, which produces a biochemical imprint for growth control, requires infrequent dosing to restrain neoplastic growth in vivo.