The effects of surfactants on the efficacy of hydrogen cyanamide (H 2 CN 2 ) applied to `Perlette' grapevines ( Vitis vinifera L.) grown in the Coachella Valley of California were examined in 1994 and 1995. Vines were pruned in mid-December in both years and treatments applied at 1000 L·ha -1 the following day to dormant spurs and cordons using a hand-held spray wand. In 1994, H 2 CN 2 was applied at 0.5%, 1%, or 2% by volume in combination with 0%, 0.5%, 1%, 2%, or 3% by volume of the amine-based surfactant Armobreak. In 1995, H 2 CN 2 was applied at 0.5%, 1%, or 2% by volume in combination with Armobreak at 0% or 2% by volume. In 1994, budbreak rate was highly dependent upon H 2 CN 2 concentration when 0% to 1% Armobreak was used; budbreak was generally most rapid for vines treated with 2% H 2 CN 2 and slowest for vines treated with 0.5% H 2 CN 2 . When 2% or 3% Armobreak was used, however, little effect of H 2 CN 2 concentration was observed. Results were similar in 1995, but the budbreak of vines treated with 2% H 2 CN 2 + 2% Armobreak lagged behind that of vines treated with 1% H 2 CN 2 + 2% Armobreak. The number of days after treatment required for 70% bud-break generally declined as the concentrations of H 2 CN 2 and Armobreak were increased. A separate experiment conducted in 1995 revealed that several surfactants varying in chemical composition, Armobreak, Activator 90 and Agridex, had similar effects on H 2 CN 2 efficacy. The results indicate that the addition of surfactants to H 2 CN 2 solutions can significantly reduce the amount of active ingredient necessary for maximum efficacy on grapevines. Chemical names used: hydroxypolyoxyethylene polyoxypropylene ethyl alkylamine (Armobreak); alkyl polyoxyethylene ether (Activator 90); paraffin petroleum oil (Agridex).