The present invention provides a novel Semaphorin having neurite-outgrowth inhibition activity or proteins analogous thereto, peptide fragments of, or antibodies against, such proteins, genes encoding such proteins, expression vectors for said genes, transformed cells into which said expression vectors have been introduced, methods for producing a recombinant protein which employ said transformed cells, antisense nucleotides against the above genes, transgenic animals involving insertion or deletion of the above genes, and screening methods for antagonists of the above proteins, all of which are useful mainly in diagnoses, treatments, or studies relating to neurological diseases. The present invention further provides use of such proteins, peptides, antibodies, genes, or antisense nucleotides as pharmaceutical or diagnostic agents or laboratory reagents.