A convenient method for the synthesis of N-substituted-N'-arylcarbonylthioureas under solvent-free conditions has been developed. Ammonium thiocyanate and acid chlorides were mixed, and stirred at room temperature without a solvent, to give the corresponding isothiocyanates, which reacted smoothly with arylamines to produce the aryl(alkyl)carbonylthioureas in good yields. Unusually large values of ⁵ J _FH=12.2–15.1 Hz are observed for 1-(2-fluorobenzoyl)-thiourea derivatives, which provide information about the Ar-C-N-H torsions in these compounds.