Naïve CD4+ T cells may differentiate into a number of subsets including T helper 1 (Th1) Th2, Th3, Th17 and T regulatory (Treg) cells depending on the type of antigen they encounter. These CD4+ families have been defined based on the array of cytokines they produce and the effects they have on adaptive immune responses. CD4+ subsets are cross regulatory and at times cooperative. The study of these adaptive immune modulators has revealed the important role that cytokines play in mounting effective as well as detrimental immune responses to pathogens. Examining the cytokine responses of lymphocytes in culture can provide important understanding of how immune responses to pathogens are orchestrated. For this purpose the in vitro cytokine production of peripheral blood mononuclear cells (PBMC) from healthy dogs was examined in response to stimulation with antigens from a common canine virus (canine distemper virus, CDV), a commensal skin yeast of dogs (Malassezia pachydermatis) and a common canine helminth (Toxocara canis (T. canis)). Cell culture supernatants were removed from antigen stimulated and unstimulated control PBMC after 4, 24, 48 and 72 h and the concentration of Th1 type cytokines (IL-2, IFN-gamma, TNF-alpha) and Th2 type cytokines (IL-4, IL-5, IL-10) was determined using sandwich ELISA assays. CDV induced low levels of cytokine production initially with a predominance of IL-10 at 24h and a balanced response at 48 h of incubation. Malassezia antigen stimulated an early type 2 cytokine response with dramatic production of IL-4 at 24h of incubation compared to the other stimulants examined. By 48 h of incubation, however, the cytokine mix in response to Malassezia had also moved toward a Th1 type response. T. canis induced early production of Th2 type cytokines with IL-5 predominating; however, with longer incubation (48-72 h) there was a switch to a balanced Th1/Th2 response. In conclusion, the cytokines produced in vitro by canine PBMC in response to prototypical Th1 and Th2 type pathogens were not clearly polarized and shifted over time. While the in vitro study of PBMC cytokine responses cannot be directly extrapolated to in vivo responses to the same antigens, the results do highlight the dynamic and fluctuating nature of cytokine production.