The effect of D‐Arg‐1, D‐Trp7,9, Leu11‐substance P (SP) (spantide), a putative SP antagonist, on SP‐induced facilitation of the flexion reflex was examined. The drugs were injected intrathecally (i.t.) in decerebrate, spinalized, unanaesthetized rats. Substance P (10 ng) caused an increase in reflex magnitude for about 5 min. Spantide (10 ng and 100 ng) also caused a facilitation of the reflex that was similar to SP. Spantide (10 ng) plus SP (10 ng) also had a similar excitatory effect. One microgramme of spantide totally blocked the flexion reflex, which could not be reversed by SP, L‐glutamate, L‐aspartate or naloxone. It is concluded that spantide does not have an antagonistic effect on SP‐induced changes in spinal reflex excitability. Some of the effects of i.t. spantide observed in behavioural studies may be due to a non‐specific spinai motor block. It is suggested that the flexion reflex in the decerebrate, spinalized rat is a useful physiological model in studies of the effects of algesic and analgesic drug