An optical falling needle rheometer was employed to measure the melt viscosity of high density polyethylene (HDPE) and low molecular weight poly (tetrafluoroethylene) (PTFE). The temperature dependence of the melt viscosity of these two polymers was obtained and described by an empirical Arrhenius relation. At the present time, this method has been confirmed to be a simple and fast (within several tens of seconds for each measurement) approach to determine polymer melt viscosities of up to at least 1×105 Pa s. The sample cell containing ∼ 2.5 cm3 materials can be vacuum sealed and disposed of without the need of subsequent cleaning each time, which could be a useful feature. In comparison with HDPE, the PTEF sample melt was found to show a much higher melt viscosity with about the same degree of polymerization. © 1993 John Wiley & Sons, Inc.