The cyclic hydrocarbon, cyclopropane is obtained when carbon monoxide is hydrogenated over a silica supported rhodium catalyst, in the presence of tetravinylsilane, TVS. The cyclopropane derived from the C-13(2)-labelled TVS, Si((CH)-C-13=(CH2)-C-13)4, is almost entirely (C2CH6)-C-13-C-12, showing it to be formed from one vinyl of TVS and a surface C1 species derived from CO. This finding lends support to the intermediacy of surface methylene in the Fischer-Tropsch reaction and illustrates a new synthetic potential for such reactions.