The interaction of Fas (Apo-1) and TNF receptor-1 with their respective ligands can lead to cell death. The so-called death domain, a sequence motif present in the cytoplasmic portion of the two receptors, has been identified as a critical structural element involved in signal transduction that leads to apoptosis. Here we describe several additional proteins which contain a death domain. Novel members of this family include proteins known to be implicated not only in apoptosis but also in neuron guidance.