Control of growth and differentiation during mammalian embryogenesis is regulated by growth factors from embryonic and/or maternal sources. Cytokines are polypeptide growth factors that are released by a variety of activated immune and nonimmune cells. To identify novel members of the cytokine family that could be involved in the growth and differentiation of the preimplantation embryo, we studied the expression pattern of several genes encoding cytokines and their receptors during mouse preimplantation development in vitro We found that poly(A)+ mRNAs for IL‐1, IL‐3, IL‐6, IL‐7, and TNFα are differentially expressed at several stages of mouse preimplantation development, including unfertilized oocytes. Immunostaining of preimplantation embryos using monoclonal antibodies specific for several cytokines and their receptors revealed that at least some of these mRNAs are translated into mature proteins during preimplantation development (IL‐1, IL‐6, and TNFα). Positive staining for IL‐1 and IL‐6 receptors was also detected at these stages of development. The controlled expression of these “inflammatory‐type” cytokines and their receptors suggests a role for these growth factors during the early phases of mouse ontogeny.