Treatment of poly(pyridine-2,5-diyl) PPy, poly(quinoline-2,6-diyl) P(2,6-Q), and poly(naphthyridine-2,6-diyl) P(2,6-N) with H2O2 in acetic acid gives quantitatively N-oxidized products of the polymers, PPy-ox, P(2,6-Q)-ox, and P(2,6-N)-diox, respectively. pi-pi* absorption bands of the original polymers show a hypsochromic shift by 35-50 nm by the N-oxidation. Treatment of PPy and P(2,6-Q) with tetracyanoethylene oxide affords N-ylidated products with a 10-15% degree of N-ylidation. The N-oxidized and ylidated polymers undergo electrochemical reduction in a range of about -1.7 to -2.2V vs Ag/Ag+. The electrochemical reduction is accompanied by colour change, and colours of the reduced polymers are considerably different from those of the original polymers (e.g. PPy). The N-oxidized and -ylidated polymers have a d.c. electrical conductivity of 2.8 x 10(-7)-3.4 x 10(-6) S cm(-1).