This paper reviews the evidence indicating possible roles for tumour n
ecrosis factor-alpha (TNF alpha) in development. It is proposed that T
NF alpha may have essentially three major roles during embryonic devel
opment, which may be analogous to its roles in the immune system and d
uring inflammation: a role in programmed cell death; a role as a cellu
lar growth and differentiation factor; and also a role in the remodell
ing of extracellular matrix, and the regulation of cell adhesion molec
ules and integrins. The concept of the existence of a cytokine array d
uring embryogenesis, analogous to that occurring in inflammation, is d
iscussed, as well as potential roles for TNF alpha in the induction of
ubiquitin; protective mechanisms embryonic cells may employ against T
NF alpha-mediated cytotoxicity; and a consideration of the role TNF al
pha may play in a ''free radical theory of development''.