The u.v. hypochromy of poly(2-vinylpyridine) of different degree of isotacticity, atactic poly(2-vinylnaphthalene) and polyacenaphthylene in relation to 2-ethylpyridine, 2-ethylnaphthalene and acenaphthene, respectively, was evaluated. In the case of poly(2-vinylpyridine) the hypochromic effect was greater for an isotactic-rich sample (8.2%) than for an atactic one (4.8%). The decrease in absorption intensity of polymers containing naphthalene chromophores was compensated by broadening of the u.v. bands and the hypochromy was relatively small : 4.7% for poly(2-vinylnaphthalene) and 4.3% for polyacenaphthylene.