Nineteen indicator systems were examined as potential alternative spot-tests for preservative penetration in TnBTO- (bis-tributyltin oxide) or AAC- (alkyl ammonium compound) treated wood. Results indicated phenylfluorone as an acceptable alternative to pyrocatechol violet for assessment of TnBTO, and cobaltous thiocyanate or a bromocresol green/quinine sulphate mixture as alternatives to bromophenol blue for an AAC.