Pressure on the skin of the tail base and perineum of female rats in the range of 40--440 millibars, following bilateral contact with the flanks, was adequate to elicit the lordosis reflex. Hair deflection alone or noxious stimulation was neither sufficient nor necessary for lordosis behavior to occur. 2. For a given pressure, increasing the area of stimulation increased the effectiveness for evoking lordosis; inputs from mechanoreceptors at different skin locations can be summated to trigger the behavioral response. 3. During mating behavior, increased pressure from the male rat on the skin of the female, in the range of 50--450 millibars, was associated with increased probability and strength of lordosis. 4. Increasing the dose of estrogen increased the probability of lordosis to a given pressure stimulus. The hormone effect can be characterized as a facilitation of the throughput from low-threshold pressure receptors on tail base and perineum to motoneurons for the lumbar vertebral dorsiflexion of lordosis.
