It has been shown that catalytic amounts of tris(triphenylphosphine)chlororhodium(I), RhCl(PPh3)3, in benzene, dichloromethane, or chloroform solution will convert monosubstituted α-hydroxyacetylenes predominantly into the dimers. In this way 3-methylbut-1-yn-3-ol yields 2,7-dimethyloct-3-en-5-yne-2,7-diol; by analogy dimers were obtained from 3-methylpent-1-yn-3-ol, but-1-yn-3-ol, and 1-ethynylcyclohexan-1-ol. Although phenylacetylene gives some 1,4-diphenylbutenyne, it also yields higher polymers. Equal quantities of methylbutynol and phenylacetylene give a mixture from which 5-methyl-1-phenylhex-3-en-1-yn-5-ol can be isolated. The new compounds are characterised by i.r. and n.m.r. spectroscopy. A metal complex was obtained in one case, being bis(triphenylphosphine)(2,7-dimethyloct-3-en-5-yne-2,7-diol)chlororhodium(I).