Far-UV (200-320 nm) radiation regulates development in plants and fungi. Some of these responses are controlled by a chromophore which absorbs strongly near 260 nm, possibly a nucleic acid. Other responses are controlled by a chromophore(s), with maximal in vivo sensitivity near 295 nm. In plants, far-UV induces genes in the phenylpropanoid pathway and the synthesis of phytoalexins and flavonoids. Far-UV also regulates growth rate, controls curvature and taxis, and stimulates sexual and asexual morphogenesis of fungi. Some of these developmental responses may prevent damage by far-UV radiation.