Human neuronal growth inhibitory factor (hGIF) is able to inhibit the out-growth of neurons. As compared with the amino acid sequences of metallo-thionein 1⁄2, hGIF contains two insertions: a Thr at position 5 and an acidic hexapeptide EAAEAE(55–60) close to the C-terminus. Moreover, all mammalian growth inhibitory factor sequences contain a conserved CPCP(6–9) motif.