To prevent corrosion tri-cresyl-phosphate (TCP) is added to aircraft engine oil. TCP is a neurotoxic agent. The ortho isomers of TCP are known to be the most neurotoxic, however at present it is unknown in what concentration the ortho and the other isomers occur in cabin air. Fumes containing TCP's from engine oil can enter the aircraft due to leakage into the air conditioning system, and TCP's may be present in engine exhaust fumes. Various professions of airline staff may be exposed to concentrations of TCP: pilots, cabin attendants, ramp handling staff and ground mechanics. This research describes the assessment of the exposure through measurement inside the cockpit during flight, spot measurement on the ramp and personal measurement of ground mechanics. The research was carried out using dedicated sampling techniques and analysis using gas-chromatography coupled to mass-spectrometry. Results show that the ortho isomers of TCP were not detected. Exposure to TCP was evaluated against internal exposure limits. It was concluded that the calculated exposure was below these limits, with one exception. The exposure of the mechanics that check the oil may incidentally be close to or exceed the internal exposure limit.