Deoxyguanosine kinase, which catalyses the phosphorylation of deoxyguanosine to form deoxyguanosine 5'-monophosphate, was purified 1024-fold from extracts to newborn-pig skin. This activity requires the presence of a bivalent cation and a nucleoside triphosphate, which functions as a phosphate donor, ATP being twice as effective as CTP or GTP and 4 times as effective as UTP. The enzyme appears to have a molecular weight of 58500 as determined by Sephadex-column chromatography. Optimal enzymic activity was observed at pH 8.0; however, the enzyme remained active over a broad pH range of 5.5-9.0. Several deoxyribonucleoside and ribonucleoside monophosphates and triphosphates were tested as effectors of catalytic activity. Effective inhibitors were dGMP [Ki(app.) = 7.6 x 10(-5) M] and dGTP [Ki(app.) = 2.1 x 10(-5) M]. Both of these inhibitors acted in a competitive manner. A Km(app.) of 3.2 x 10(-7) M was measured for deoxyguanosine and a Km(app.) of 3.3 mM was determined for MgATP. Of the four major deoxynucleosides tested, this catalytic activity appears to phosphorylate only deoxyguanosine; thus the enzyme is a specific deoxyguanosine kinase.