The H atom adducts of 2,2`-, 2,4`- and 4,4` bipyridines were produced pulse radiolytically. The absorption spectra of these indicate that apart from addition at nitrogen atom the hydrogen atom adds at the ring carbon also to a lesser extent in protonated bipyridines. Regular variation of absorption spectra of H adducts of these three isomers were observed. (author). 4 refs., 1 tab.