The rate of blood flow in the skin has relevance to a several cardiovascular conditions of clinical significance. There is no accepted fast, easy way to noninvasively measure the volumetric rate of blood flow per unit tissue volume however. Previous work has suggested the potential for using skin heating from radio frequency (RF) energy in the millimeter wave (MMW) band, with simultaneous monitoring of skin surface temperature for noninvasive skin temperature measurement. This work discusses feasibility and in vitro test results using a prototype transducer for MMW blood flow measurement. The transducer consists of microstrip antenna and a mid-infrared temperature sensor integrated in a thermoplastic housing. The prototype was tested in a controlled flow chamber, using a commercial tissue phantom material,at flow rates ranging from 0.25 ml·min-1 to 20 ml·min-1, equivalent to approximately 10 to 800 ml·min-1·per 100 cm3 of tissue. The differences in temperature increase at exposure time t=60 "s" were statistically significant (n = 5) so as to allow resolution of flow rates of 0.25, 0.50, 1.0, 2.0, 10 and 20 ml·min 1. The temperature increase vs time over the 60 s exposure window is described by a simple two-parameter model which can be correlated with the flow rate. The flow rate model parameter does not scale directly with the flow in the experimetal chamber however. This may suggest limitations either in the model or the experimental procedure.