A computerized tensimeter and experimental procedure for determination of the thermal decomposition temperature (Td) of perfluoroalkylethers have been developed and tested. Both the apparatus and the procedure are described in detail. Results of testing with bis (2-ethylhexyl) phthalate and trimethylolpropane triheptanoate demonstrate that the reciprocal of the decomposition temperature is a linear function of the logarithm of the gas volume/heated liquid volume ratio. The Td obtained for each compound at a gas volume/heated liquid volume ratio of one was similar to the value previously reported using an isoteniscope technique. Results of testing with a polymer of hexafluoropropylene oxide demonstrate that this instrument and procedure can be used to determine the Td of perfluoroalkylethers.