A subset of serum samples from dogs with lymphoma (n = 25) and healthy dogs (n = 20) were evaluated with four different TK1 assays, two of which were based on TK1 activity measurements (DiviTum assay Biovica, Uppsala, Sweden and dThd phosphorylation assay) and two immunoassays (Canine TK1 ELISA and AroCell TK 210 ELISA, Arocell, Bromma, Sweden). Here, TK1 is linked to lymphoma.