Abstract 2,3-Dimethylbicyclo[2.2.1]hept-2-en-7-yl and 6-methyl-1,4-dihydro-1,4-methanonaphthalen-9-yl radicals are examined wiht ESR. Comparisons of their hyperfine splitting constants with those of bicyclo[2.2.1]hept-2-en-7-yl (1a) and 1,4-dihydro-1,4-methanonaphthalen-9-yl (2a) radicals show that the odd electron on the tervalent carbon atom is delocalized to the extent of 10% into the π system of the vinylene bridge in 1a, and 5% at maximum into the π system of the phenylene bridge in 2a, respectively. This odd eletron delocalization is accompanied by an increase of carbanion character of the tervalent carbon atom. The nonplanarity of their tervalent carbon atoms is discussed in relation to the carbanion character.