The addition of a hardener is necessary for the curing of urea-formaldehyde (UF) adhesives in the production of MDF and particleboard. The most commonly used hardener, ammonium chloride, however, is suspected to cause the formation of poisonous dioxin when waste boards are combusted and hence considered as a potential source of pollution. To assess the feasibility of substituting ammonium sulphate for ammonium chloride, working properties and bonding strength were measured for UF adhesives with the two hardeners at different levels of concentration. It was found that the effects of the two hardeners are practically identical on the pH, gelation time and viscosity and bonding strength, all other conditions being the same. Both ammonium chloride and ammonium sulphate can be easily handled in the same way, and therefore there is no need to modify the application method and equipment. The practical and economical implications of these findings suggests that ammonium sulphate is an appropriate alternative to The addition of a hardener is necessary for the curing of urea-formaldehyde (UF) adhesives in the production of MDF and particleboard. The most commonly used hardener, ammonium chloride, however, is suspected to cause the formation of poisonous dioxin when waste boards are combusted and hence considered as a potential source of pollution. To assess the feasibility of substient ammonium sulphate for ammonium chloride, working properties and bonding strength were measured for UF adhesives with the two hardeners at different levels of concentration. It was found that the effects of the two hardeners are practically identical on the pH, gelation time and viscosity and bonding strength, all other conditions being the same. Both ammonium chloride and ammonium sulphate can be easily handled in the same way, and therefore there no no need to modify the application method and equipment. The practical and economical implications of these findings suggests that ammonium sulphate is an appropri ate alternative to