Available data from our and other laboratories on the presence and biological functions of cytokine‐ and growth factor‐like molecules in invertebrates are reviewed. It appears that IL‐1α‐, IL‐1ß‐, IL‐2‐, IL‐6‐, TNF‐α‐like molecules and haemokinin are present in several cell types from molluscs, insects, annelids, echinodems and tunicates. In most cases, these molecules are present in cells with phagocytic activity and they modulate cell motility. PDGF‐, TGF‐ß‐, EGF‐ and NGF‐like molecules, growth promoting factors and the hemolymph trophic factor are present in several cell types from molluscs, insects and annelids. These molecules are probably involved in the control of cell proliferation. Both cytokines and growth factors appear to be highly ancestral and biologically very important molecules, as evident from their continuous presence from invertebrates to vertebrates. It also appears that cytokines are functionally conserved molecules, which during evolution have also maintained their pleiotropicity, redundancy in mode of action and the promiscuity of their receptors.