Tri-p-cresyl phosphate is a nonneurotoxic regioisomer of tri-o-cresyl phosphate and a congener of tri-p-ethylphenyl phosphate. Patch tests (triphenyl phosphate allergy) with analytical grade triphenyl phosphate, tri-m-cresyl phosphate, and tri-p-cresyl phosphate in the concentrations 5%, 0.5% and 0.05% pet. showed positive reactions to 0.05% triphenyl phosphate and 0.5% tri-m-cresyl phosphate, but no reaction to tri-p-cresyl phosphate.