Fully regioselective synthesis of 5-hydroxyethylpyrazoles was exploited by reacting hydrazonoyl chlorides with homopropargylicalcohols in the presence of catalytic amounts of copper(I) chloride. Good yields of pyrazolic products and mild reaction conditions were experienced notwithstanding the known, poor reactivity of homopropargylicalcohols towards hydrazonoyl chlorides. The role of copper(I) ion