The results obtained on thermal stability and reactions of CyHy hydrocarbon fragments on metal surfaces are discussed. CxHy species are produced by thermal and photo-induced dissociation of corresponding iodo compounds. Whereas CH3 and CH2 are mainly converted into CH4 on Pt metals at 140-180 K, they recombine readily to yield C-2 compounds on Ag and Cu surfaces. The C2H5 reacted to form C2H4 and C2H6 on metal surfaces at 160-230 K. Effects of additives and coadsorbed species on the reactions of CxHy moieties are also examined.